Spray a 9x13" baking pan with non-stick cooking spray and set aside.
Preheat oven to 400 degrees.
In a large saucepan, combine cream of chicken soup, milk, butter, onion, garlic powder, and salt and pepper.
Stir together and cook over medium heat until heated through.
Remove saucepan from the heat and stir in chicken, mixed vegetables, and cheese.
Scoop mixture into prepared pan. Top with frozen tater tots.
Bake for 25-30 minutes or until casserole starts to bubble.
Notes
If you want to turn this into a freezer meal, prepare casserole as directed, but place in a freezer-safe pan and cover with aluminum foil before baking. Keep in the freezer for up to 3 months.
Remove from freezer 30 minutes before baking. Preheat oven to 350 degrees and bake for 90-100 minutes or until heated all the way through.
You could also make this in 2 8x8" pans and put half of the casserole into the freezer to save for another night and cook the other casserole to enjoy tonight!