Spray 3- to 4-quart slow cooker with cooking spray. In cooker, gently mix thawed meatballs, pasta sauce and peppers.
Cover; cook on Low heat setting 6 to 8 hours.
Place 2 cheese half-slices on bottom half of each bun. Spoon about 5 meatballs and sauce over cheese on each. Sprinkle each with about 1/2 teaspoon basil. Cover with top halves of buns.