1. Prepare grill.
2. Coat both sides of steaks with cooking spray. Sprinkle both sides of steaks evenly with herbes de Provence, 3/4 teaspoon salt, and 1/2 teaspoon black pepper.
3. Coat both sides of the onion slices with cooking spray. Sprinkle the onion slices with remaining 1/4 teaspoon salt and remaining 1/4 teaspoon black pepper.
4. Place steaks and onion slices on grill rack coated with cooking spray; grill 4 minutes on each side or until steaks are at desired degree of doneness and onion is tender. Remove from grill; cover and let stand 5 minutes. Cut steaks diagonally across grain into thin slices; discard bones. Serve steak with onion.