Heat the garlic cloves in olive oil over a low heat in a medium skillet.
Char the bread slices under a hot broiler so that they're brown on both sides. Use a pastry brush to dab the toasted bread with olive oil.
Take the unused oil and combine it in a small bowl with the olives.
Place the garlic cloves on a cutting board and pile them with the capers, pepper flakes, and rosemary leaves. Chop the garlic and herb mixture and combine it with the olives in a small bowl.
Assemble the crostini by spreading it with olive tapenade on the toasts.