Preheat an oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
Combine the cream of mushroom soup, cream of chicken soup, sour cream, seasoned salt, and pepper. Stir in the mixed vegetables and onion. Add the tater tots and stir until they are coated with the mixture. Pour into the prepared baking dish. Press the meatloaf slices into the top of the tater tot mixture.
Bake in preheated oven 15 minutes; sprinkle the Cheddar cheese over the top, and bake 35 minutes until the cheese browns. Remove from the oven and let stand 10 minutes before serving.