Flatten chicken to 1/4-in. thickness. Sprinkle with 1/4 teaspoon lemon-pepper and salt; set aside.
In a large skillet, saute onion in oil and butter until tender. Sprinkle with the garlic powder and remaining lemon-pepper. Remove the onion and 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 and simmer for 2-3 minutes or until the marmalade is melted and chicken juices run