Slice the garlic, mozzarella, tomatoes, peppers and basil; set aside separately. Rub one side of each slice of bread with a cut side of garlic and brush with oil. On the other side of 4 slices, layer the cheese, tomatoes and peppers; assemble sandwiches with oiled sides facing out.
Place 2 sandwiches in a large pan over medium-low heat. Cover and cook for 6 minutes or until golden brown and cheese is melted, turning sandwiches once. Repeat with remaining sandwiches.
Tuck a few slices of basil into each sandwich. Sprinkle with salt and pepper.
Serve with any remaining peppers and sliced plums.