On a wooden skewer, thread 1 piece corn, 1 onion and 1 tomato. Repeat until skewer is filled, leaving a 1-inch space at the end.
Lightly spray pan with cooking spray. Spray kabobs with cooking spray and season with salt and pepper. Place kabobs on grill, and cook until heated through, turning occasionally to create grill marks on all sides, about 10 minutes in all. Serve immediately.