Rinse both sides with cold water and place flesh side down on dish towel.
In a bowl, mix all marinade ingredients together.
Lay out mushrooms and onion in a baking dish. Pour marinade over. Coat well. Leave for 30 minutes.
Slice peppers and marinate in olive oil, red wine vinegar. Yellow or orange peppers to keep the dish bright!
Wash and set aside your lettuce ‘bun’.
After you have let your mushrooms and onions marinate for 30 minutes, set oven to broil. You could also use the bbq or stove top. Place mushrooms, onions, and peppers on rack. Pour the left over marinade from your baking dish and broil for about 8 minutes. No need to flip as you will lose some of the delicious marinade.
Place mushroom, onion, peppers, on lettuce bun. Top with tomato, avocado, tzatziki, hot sauce, sprouts, etc..