In a large pot, add soup, milk, butter, thyme, garlic powder, onion powder and pepper. Cook and stir over medium heat until heated thru and butter has melted. Remove from heat.
Stir in chicken, peas and carrots, corn and 1 cup shredded cheese. Transfer to one greased 9 x 13 freezer-safe baking pan, or 2 greased 8 x 8 freezer safe baking pans.
Spread frozen tater tots over chicken mixture in a single layer. Top with remaining 1/2 cup cheese.
Cover pan(s) with foil, then wrap in plastic. Freeze for up to 2 months.
To Bake Right Away:
Assemble casserole thru Step 3, but do not top with cheese at this point.
Bake in 400°F oven for 25 to 30 minutes until sauce is bubbling.
Top with remaining 1/2 cup cheese and bake an additional 5 minutes until cheese is melted.
To Bake From Frozen:
Remove pan from freezer 30 minutes before baking. Remove plastic wrap.
Preheat oven to 400°F.
Bake covered for 1-1/2 hours, remove foil and continue baking for an additional 30 minutes until tater tots are golden brown and casserole is heated thru.