1. Cut 4 sheets heavy duty aluminum foil in 12-inch squares. Spray each sheet with non-stick cooking spray. Heat grill to Medium-High heat. Cut steak into 1/8-inch strips, sprinkle with salt and pepper.
2. Center 1/4 of onions on non-stick foil sheet (dull side up). Top with 1/4 of the steak and cheese. Bring up foil sides. Double fold top and ends to seal. Make 4 packets.
3. Grill 8 to 10 minutes in covered grill. Serve on rolls with additional cheese and ketchup.