1In 10-inch nonstick skillet, heat oil over medium-high heat. Add chicken; sprinkle with salt and pepper. Cook about 5 minutes or until browned. Reduce heat to medium; add mushrooms. Cook 8 to 12 minutes, turning occasionally, until mushrooms are tender. Remove chicken and mushrooms from skillet; drain if necessary. Cover to keep warm.
2To same skillet, add gravy mix and 1 1/4 cups water. Heat to boiling over medium heat, stirring frequently with wire whisk. Return chicken and mushrooms to skillet. Reduce heat to low. Cover; cook 10 to 15 minutes or until sauce is thickened and juice of chicken is clear when thickest part is cut to bone (at least 165°F).
3Meanwhile, make potatoes as directed on box, using water, milk butter and salt. Serve chicken and mushrooms with mashed potatoes.