PREHEAT oven to 375°F (190°C).
REMOVE pie shell from freezer and thaw for 10 minutes. Meanwhile defrost frozen veggies in microwave, draining excess water.
CHOP and sauté onion.
MIX chicken, veggies, sautéed onion, garlic, soup and milk in a large mixing bowl.
POUR into pie shell; bake for about 30 to 40 minutes or until crust is golden brown and filling is bubbling.