Sprinkle chicken with salt and pepper. Heat butter and oil in a large nonstick skillet coated with cooking spray over medium-high heat. Add chicken to pan; cook 4 minutes on each side or until lightly browned.
Combine orange marmalade, cornstarch, lemon juice, and mustard in a small bowl, stirring mixture well with a whisk. Gently stir in oranges. Add marmalade mixture to pan; cover and simmer 6 minutes or until the sauce is slightly thick, stirring once.