Slice tomatoes and mozzarella cheese in slices and set aside. Mix the olive oil, balsamic vinegar, garlic, salt & pepper and marinate the portobello mushroom caps in this marinade for 10 minutes. Chop the lettuce leaves in half and set aside. Grill the portobello mushrooms for 3 minutes per side and on the last minute, grill D’ Italiano brioche buns for a minute, cut side down. Top each side of the with pesto, and add a few slices of tomatoes, fresh mozzarella and lettuce.