Method:
Prepare a grill for medium-high heat cooking. Brush bread with 1 teaspoon of the oil and grill until nicely marked, about 1 minute per side. Rub bread slices on both sides with garlic; discard clove. Set bread aside.
Place romaine, tomatoes and onions on a baking sheet. Drizzle with 1 tablespoon of the oil and rub until vegetables are coated all over. Grill, turning vegetables frequently with tongs; cook lettuce until outer leaves are just browned and softened, 4 to 5 minutes, and tomatoes and onions until softened and slightly charred, 7 to 8 minutes. Transfer vegetables back to the baking sheet as they are done.
In a small bowl, combine vinegar, salt, pepper and remaining 2 tablespoons oil. Thinly slice romaine, place on a large platter and drizzle with half the vinaigrette. Very coarsely chop tomatoes and onions, place in a large bowl and toss with remaining vinaigrette. Pile tomato mixture over lettuce and sprinkle with oregano. Cut bread into large chunks and arrange around edges of platter.