Thinly slice bread, remove crusts and cut into enough 1/2" croutons to make 1 cup.
In a skillet, warm the olive oil, add the croutons, and saute until golden; drain on paper towles.
Cut tops off peppers about 1/2" from top, and reserve tops. Carefully remove seeds and membranes.
In a bowl combine croutons, mozzarella, basil, garlic, and oil. Mix well, adding salt and pepper to taste. Stuff peppers with mixture, replace tops and secure with toothpicks.
Grill peppers, top sides up, overf indirect medium heat until peppers are soft but still hold their shape, 12 to 15 minutes.