Flatten chicken to 1/4-in. thickness; sprinkle both sides with salt and pepper. In a large nonstick skillet, brown chicken in oil and butter over medium heat for 3-5 minutes on each side or until a thermometer reaches 170°., In the same skillet, whisk the lemon juice, parsley and mustard until blended. Whisk in broth and green onions; heat through. Serve with chicken.