1Heat oven to 375°F. In small bowl, mix cheese, mayonnaise and onions. Spread about 1 teaspoon cheese mixture on each bread slice; place on ungreased cookie sheet. Top each with half slice of bacon.
2Bake 10 to 12 minutes or until edges of bread are golden brown and cheese is melted.
3Garnish each crostini with lettuce and tomato slice.