Chicken Pot Pie

1 lb Boneless Skinless Chicken Breast
1/4 cup chopped onion
1/4 cup chopped celery
1/4 cup butter
1/4 cup flour
1/4 tsp garlic powder
1/8 tsp ground thyme (or 1/4 tsp if not ground)
1/8 tsp pepper
14.5 oz can chicken broth
1 1/2 cup frozen mixed veggies
1 refrigerated pie crust
1 egg beaten (optional)

In a large skillet over medium heat, heat 1 1 tbs olive oil/ Add onion, celery, and chicken. Cook until chicken is no longer pink. Remove chicken and veggies from skillet. Melt butter in same skillet. Stir in flour, garlic powder, thyme, and pepper. Cook until smooth and bubbly. Gradually add chicken broth, stirring constantly until mixture boils and thickens. Add cooked chicken mix and frozen mixed veggies. Simmer until heated through. Spoon into pie pan. Place pie crust on top of chicken mixture. Flute edges and cut a few slits in several places. Brush on egg if desired.  Bake @ 425 degrees for 25-30 minutes, or until crust is golden brown.