Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Sprinkle chicken with salt and black pepper. Add chicken to pan; cook 4 minutes on each side or until lightly browned. Remove from pan; keep warm.
Add sherry, sugar, soy sauce, vinegar, and red pepper to pan; scrape pan to loosen browned bits. Bring to a boil; cook 1 minute. Stir in oil.