Flatten chicken to 1/4 in. thickness. Sprinkle with 1/4 tsp. lemon pepper & salt; set aside.
In a large skillet, saute onion in oil & butter until tender. Sprinkle with the garlic powder & remaining lemon pepper. Remove the onion & keep warm.
In the same skillet, cook chicken over medium heat for 3 minutes on each side or until browned. Spread marmalade over chicken. Return onion to the pan. Reduce heat; cover & simmer for 2-3 minutes or until the marmalade is melted & chicken juices run clear.