In a small bowl, combine the garlic and EVOO. Let sit while you prep and grill the bell peppers.
Preheat a grill to medium-high. Cut the bell peppers into flat panels. (Discard the stems, cores and seeds.) Lightly oil the grill grate and grill the pepper pieces, covered and turning occasionally, until just softened, about 10 minutes. When cool enough to handle, cut into 1-inch squares and transfer to a medium bowl. Stir in the tomatoes, onion and vinegar; season with salt and pepper.
Brush the bread slices on both sides with the garlic oil. Grill, turning once, until well marked and toasted, 2 to 4 minutes. Cut into large cubes.
Stir the remaining garlic oil into the salad. Add the croutons, mozzarella and basil; toss.