Healthy Burgers? 5:2 Diet and Healthy Portobello Mushroom Burger

Healthy Portobello Mushroom Burger:

portabello mushroom burger cut - side

OK, I fibbed just a bit.  You probably CAN’T quite have your burger like this on a 5:2 diet fast day.  The bread roll adds a wopping 150 calories.  But, it’s just as delicious (though not quite as photogenic) without the bread, or with just the base, like a burger open sandwich.

And, portobello mushrooms make excellent meat substitutes.  There’s nothing particularly difficult in this recipe and it’s perfectly acceptable to mix and match the toppings according to your own personal preference.  I used a slice of low calorie leerdammer cheese which melts beautifully and has around 50 calories a slice but you could crumble a little blue cheese or add a slice of grilled bacon.  It’s up to you!

The mushroom itself has around 30 calories.  You will be adding a little oil to marinade and grill it and of course the mixture of toppings.  So the final dish, without bun and using just mustard and low calorie mayo is around 200 calories. Add the bun and you are still only hitting 350 calories. It just doesn’t feel like diet food though.

Portobello Mushroom Burger – 5:2 Diet Plus

Serves 1
Prep time 15 minutes
Cook time 15 minutes
Total time 30 minutes
Allergy Egg
Dietary Vegetarian
Meal type Lunch, Main Dish
Misc Serve Hot


  • 1 Large Portobello Mushroom
  • 1 thin slice Leerdamer light cheese (Or similar)
  • 2 teaspoons Balsamic vinegar
  • 2 teaspoons Olive oil
  • 1/2 teaspoon Rose Harrissa
  • 1/2 Medium Red Onion (finely sliced)
  • 1 teaspoon Olive oil
  • 1 thin slice Tomato
  • 1 teaspoon Low Calorie Mayo
  • 1 handful Salad Greens
  • 1 Burger Bun


Step 1 Mix the balsamic, 2 teaspoons of oil and rose harissa. Use to baste the mushroom and put to one side for 20 minutes or so
Step 2 Gently fry the red onion in a teaspoon of olive oil till caramelised. Put to one side and keep warm
Step 3 Portabello Mushrooms Grill
Grill the mushroom on a griddle or barbecue, top side up for 2-3 minutes, then turn. Baste well with whatever is left of the marinade
Step 4 Continue to grill, topping the mushroom with the cheese slice for the last 2 minutes. Put to one side and keep warm.
Step 5 Split the burger bun, grill the inside till toasted.
Step 6 Put your burger stack together. Top the base of the roll with the mushroom (cheese up), then add a good spoon of caramelised onion, then add tomato, then salad greens. If liked, add mustard, ketchup, mayo or a mixture of all three.
Step 7 Enjoy!

It’s for that reason that I’m calling this a 5:2 diet plus recipe.  It’s quite nice enough to have on a fast day, without the bun and being ultra careful with the toppings.  But, honestly, would you question this on your dinner plate any day of the week?

portabello mushroom burger ready to eat


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  1. Love mushrooms. Might try this x

  2. What a fabulous idea Fiona. We always have Portabello Mushroom with our BBQ’s but would never have thought to use it in a Burger Bun – must try this:-)

  3. Ill have to give this a try

  4. If I didn’t hate mushrooms so much I would have given this a try, fed up with the taste of burgers at the moment. Thank you for sharing. Hope you have had a lovely weekend

    Laura x x x

  5. I had one in a burger bar in Swansea Fi and yep they’re lovely. We’ve now shamelessly copied it too, I quite like adding a curry mix to mine and forgo the bun but make some spiced wedges to go with it.

  6. Fabulous meal for 350 cals! I love Mushrooms and portobello top my list maybe after chestnut mushrooms my everyday delight! I love such recipe ideas that look good are filling and yet manage to stay healthy ,win win on taste n the healthy meter!

  7. That sounds really tasty. I don’t have a griddle/grill thingy but I guess I could make it under the grill as long as it was basted with marinade, it shouldn’t dry out. Would make a great lunch, thanks for sharing.

  8. It really doesn’t look like diet food. Looks delicious and would satisfy the need for something naughty. GG

  9. I have never tried a portabello mushroom burger but I can image these lovely large mushrooms can be subbed in for lots of meat or heavier dishes.

  10. OMG! This is what I’ve been waiting for, love caramelized onions and muchrooms and this looks like a perfect combination of those two :)

  11. I WAS wondering when I saw the BREAD roll Fiona! LOL! But looks like a very tasty LOWER calorie burger than normal though! Karen

  12. Pamela Morse says:

    My partner is a meat eater in a home with no meat. He does enjoy meat at restaurants, but mushrooms do make a very good substitute. We eat this a lot.

  13. This looks great. I need to do more portobello mushrooms. It makes sense to do this bec of exactly what you said.. a great indulgence for 350 calories

  14. I love mushroom burgers as i don’t eat red meat much. Never tried it with harissa. Great idea. I like it with a slice of grilled halloumi but that prob has too many calories for 5:2.

  15. Sounds good to me Fiona and as I keep most of my calories for evening that is fine. Although I need o start doing this. Holiday piled on the pounds.

  16. Goodness that looks juicy, silky, moist, full, filling and oof, scrumptious! one worth saving myself for x

  17. Barbara Handley says:

    I would not have thought of making this although I love mushrooms. Looks delicious.

  18. Paul Anthony Gallagher says:

    This sounds tasty although would prefer meat!

  19. Amy Jo McLellan says:

    I haven’t had a mushroom burger in ages but you’ve just inspired me to have one again soon. This looks delicious!

  20. This sounds amazing! I love a good mushroom burger

  21. Sarah Lewis says:

    Always looking for ideas of what to eat on fasting days will definitely be giving this one a try.

  22. Barbara Handley says:

    I love the look of this. I am currently compiling recipes for the 5:2 diet for me to try and this will definitely be included.

  23. Wow this looks lovely. I might have to try this x

  24. Jane Middleton says:

    love mushrooms and this is such a great way for vegetarians to enjoy a barbeque too

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