1. Cook chicken and onion in butter in large skillet over medium-high heat, 5 minutes.
2. Stir in gravy mix and milk. Cook, stirring, until thickened and chicken is no longer pink. Add vegetables.
3. Spoon into 10-inch deep-dish pie plate or shallow casserole. Top with crust; fold edge under.
4. Bake at 425°F, 15 minutes or until golden brown.