Preheat the oven to 350°F. Spray the cups of a 12-cup standard size cupcake-muffin pan with cooking spray. Set aside.
In a large skillet over medium high heat, melt butter. Add flour, garlic salt, lemon pepper, onion powder and ground mustard. Whisk until butter is absorbed.
Add half and half, whisking until fully combined. Bring to a gentle bubble whisking constantly. Lower heat and let simmer for 3 minutes. Remove from heat, add chicken, vegetables and thyme. Mix well. Set aside.
Meanwhile, bring crusts to room temperature per package directions. Unroll one pie crust on a non stick or lightly floured surface. Using a 3.5-4 inch biscuit cutter, cut into 6 rounds. Repeat with second crust. Press one round onto bottom and sides of each well of cupcake pan.
Reroll scraps and cut into (12) 1.5 inch rounds.
Divide filling evenly between each of the 12 crusts. Top each mini pie with a 1.5 inch dough round. (You can repeat and reroll any leftover scraps and cut into additional shapes of 1.5 inch rounds to bake along with pot pies on a separate pan.)
Brush the top crusts with beaten egg. (Also any additional pie crust rounds you're baking separately)
Place pies into the preheat oven and bake for 25 minutes or until the crusts are golden and filling is bubbly. Let stand in pan for 3-5 minutes.
Run a knife around the edge of each pie and gently lift from the bottom to a platter. (You may place any additional crust rounds on each, if you have extra.)
Store leftovers in an airtight container chilled. You may also freeze in an airtight container after cooling for up to 2 months.
Reheat chilled pies in the microwave or frozen pies in a 325°F oven until heated through. (lay foil on top in the oven)