Set the grill to a medium heat.
Whisk together the garlic, vinegar, 1/4 tsp black pepper, 1/2 tsp salt, and 2 tbsp olive oil in a large stainless steel bowl.
Brush the remaining olive oil over the bread pieces, red peppers, and onions in the jelly roll pan; sprinkle with a little salt and black pepper.
Place the chicken, bread, peppers, and onions on the grill using tongs.
Turn the bread over and cook it for a further minute under indirect heat after cooking it covered for two minutes.
After removing the bread, flip the peppers and onion and cook for a further six minutes. Remove the peppers and onion, flip the chicken, and cook for a further 6 minutes. All items should be cut into half-inch pieces.
Toss the tomatoes, basil, vinaigrette, chicken, onion, peppers, and bread together in a basin. Serve.