Light the grill. Spray an 18-inch square piece of aluminum foil with the cooking spray.
Mix together the bell peppers, onion, garlic, Parmesan, salt, oregano, basil, parsley, and seasoning in a bowl. Transfer onto the foil and spray with the cooking spray. Seal the vegetables in the foil.
Place the foil wrapped peppers on the grill. Grill, covered, for about 30 minutes. Flip the foil pack over a few times while grilling.