Heat a grill pan over medium-high heat. Coat pan with cooking spray. Add onion; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon black pepper. Cook 8 minutes or until browned, stirring occasionally. Remove from pan; keep warm.
Combine garlic powder and next 5 ingredients (through 1/4 teaspoon black pepper) in a small bowl. Sprinkle garlic mixture over both sides of beef. Add beef to pan. Grill 5 minutes on each side or until desired degree of doneness. Serve with onion mixture.