Brush one side of each bread slice with olive oil. Place 2 slices, oil side down, on a baking sheet and layer with basil leaves, tomato slices, and mozzarella slices. Salt and pepper to taste and then top with remaining bread slices, oil side up.
Broil 6 inches from heat, turning once during cooking, until bread is golden brown and cheese is melted, about 2 to 3 minutes total. Serve immediately.