This recipe is excellent. However, I don't have a grill so the first time I broiled them on a cookie sheet with tin foil. They came out great, but I found that the marinated made them slightly runny. Next time I made them I placed them on a wire rack with a cookie sheet under it and broiled it for the same amount of time - about 5 minutes on both sides. Came out fantastic! Update: I've made these burgers so many times now, they're that good. To add some extra flavour, chop 2-3 onions and sauté them for at least 20 minutes on low heat with olive oil and butter. Viola, caramelized onions, which taste AMAZING with these burgers. One final note for those who didn't like the vinegar taste: a good balsamic is essential. The cheap stuff (under 5 bucks) is gross and overpowering. Buy a good bottle (you'll use less) and it tastes much sweeter.

Wow! The cheese really makes this a treat. I tried grilling this on my Foreman grill for just a few minutes, and it comes out perfect!

Honestly, as a real meat lover, I could replace hamburger forever with grilled portobello! The taste is beyond belief. Simplified things a bit, as some men might. Just used a dish of olive oil, added a dash of salt and pepper and brushed it on. I also did the same to 1/2" thick cuts of onion and grilled them side by side (onions a little longer of course). When they were both finished, I topped the mushroom with the thick cut onion and topped that with provilone. What a surpise I am telling you. Good luck and Thank you!

better than sex

I love this recipe and can eat this every day. I serve this on a whole grain bun with some roasted red peppers, a slice of red onion, and red (or green)lettuce. An excellent sandwich! I have also broiled the mushrooms in my toaster oven, and the results are just as good as grilling them.

Absolutely delicious! My husband was surprised at how meaty and satisfying these were. I used fresh basil as opposed to dried and they turned out great. I also only marinated them for about 10 minutes since I have had experiences in the past where the mushrooms soak up too much of the vinegar and end up tasting sour. A great vegetarian alternative!

These were pretty good. I don't have a grill so I broiled them. We ate them on a toasted French baguette, with a triple cream brie. It was lacking something so we added raw red onion, which did the trick. Next time I'll use goat cheese and add arugula.

I scaled this down to serve one (incl marinade - didn't double the vinegar), and it turned out great. Took another reviewer's advice and added fresh basil, which was delish. Swapped feta for provolone. Broiled the mushrooms (along with rings of onion to go on top) in my tiny toaster oven, and it worked out just fine. Used ciabatta bread, which I'll change next time to something less dense. Delicious, reliable marinade for mushrooms. Thanks for the recipe.

Fantastic!! I found the amount of aioli sauce to be enough for 6 portobello mushrooms. I served them on wheat buns that I basted with olive oil and grilled until lightly toasted. I also made "Baked French Fries I" from this site to go with them. To die for!! Thanks for the recipe!

My hubby loves making these. The kids think they're great and have enjoyed them also with cheddar, monteray pepper jack, and mozarella cheeses. Once the "burger" is assembled we like to top the mushroom with some marinara sauce and serve on toasted portuguese rolls. Wonderful!