Combine first 4 ingredients in a large zip-top plastic bag; add mushrooms to bag. Seal and marinate at room temperature for 2 hours, turning bag occasionally. Remove mushrooms from bag; discard marinade.
Prepare grill to medium heat.
Cut bell pepper in half lengthwise; discard seeds and membranes. Place pepper halves on grill rack coated with cooking spray; grill 15 minutes or until blackened, turning occasionally. Place in a zip-top plastic bag; seal. Let stand 10 minutes. Peel. Reserve 1 pepper half for another use. Finely chop 1 pepper half; place in a small bowl. Add mayonnaise, 1/2 teaspoon oil, and ground red pepper; stir well.
Place mushrooms, gill sides down, on grill rack coated with cooking spray; grill 4 minutes on each side. Place buns, cut sides down, on grill rack coated with cooking spray; grill 30 seconds on each side or until toasted. Spread 2 tablespoons mayonnaise mixture on top half of each bun. Place 1 mushroom on bottom half of each bun. Top each mushroom with 1 tomato slice and 1 lettuce leaf; cover with top halves of buns.
These were awesome - the red pepper sauce really made them special. As a vegetarian, I'd be thrilled if someone served these to me, but I don't think meat eaters would find the mushroom a suitable replacement to the burger - maybe the mushroom AND the burger with the sauce.
Caramelized onions and a slice of Swiss cheese (if you're not vegan) are also very special on these burgers. That's how I usually do them, instead of the mayo and roasted red pepper. (I'll have to try that, though, since it's getting such good reviews.) The marinade is what makes these so special. Brush or pour a little extra on while they're grilling. If you're cooking for one, like I usually do, a small zipper freezer bag is great for marinading.
This was easy and good. The mushrooms didn't have as much taste as I thought, nor did the mayonnaise. I ate it without a bun. I might do other condiments other than the mayonnaise, but I will make these again. Good on the grill, and a good alternative to veggie burgers!
Nice meat-free option for a simple meal. I served the portobello burgers with baked sweet potato fries and fresh melon. I cut the roasted red pepper into strips insted of putting them in the mayo. Next time I will leave out the mayo and use some goat cheese.
Who knew a die hard meat-loving husband would melt over a mushroom burger?! The marinade makes them so juicy and flavorful, and the mayo is the perfect compliment. One thing - make sure you serve them on onion rolls like stated. They're perfect for this recipe! Review and photos on my blog: http://tinyurl.com/2cphk9x