Toast the bread lightly on both sides then rub one side with the garlic. Transfer to a baking sheet.
Finely chop the olives in a blender or food processor, then add the oil and most of the basil and blend again to make a coarse paste. Spread over the garlic toasts. Cover loosely and chill until required.
When ready to serve, remove the cover and cook the toasts in a preheated oven, 190°C (375°F), Gas Mark 5, for 10 minutes. Arrange on a serving plate and sprinkle with the pecorino or Parmesan and the remaining basil leaves.