Add prosciutto; cook 4 minutes or until crisp, stirring occasionally.
Remove prosciutto with a slotted spoon.
Drain on paper towels.
Add bread to pan; cook 3 minutes or until browned, stirring frequently.
Combine prosciutto and bread.
Add remaining 1 tablespoon oil to pan.
Add tomatoes; cook 5 minutes or until skins begins to split, stirring frequently.
Pour tomatoes and olive oil into a small bowl.
Sprinkle with salt and pepper.
Preheat grill to medium-high heat.
Coat cut sides of lettuce with cooking spray.
Place lettuce, cut side down, on a grill rack coated with cooking spray. Cook 2 minutes or until well marked.
Place 1 lettuce half on each of 4 plates. Divide prosciutto mixture and tomato mixture among servings. Top each serving with 1 tablespoon onions and 1/2 ounce cheese.