Place each chicken breast half between 2 sheets of heavy-duty plastic wrap; pound each to 1/4-inch thickness using a meat mallet or small heavy skillet. Sprinkle chicken evenly with salt and pepper. Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add chicken to pan; cook 4 minutes on each side or until done. Remove chicken from pan.
Reduce heat to medium. Add onion to pan; cook 1 minute. Add syrup and remaining ingredients; cook 1 minute or until thoroughly heated, stirring frequently. Serve sauce with chicken.