Preheat Oven: Set oven to 350ºF. Lightly spray a 9×13-inch baking dish with non-stick cooking spray.

Cook Sausage: In a large skillet over medium heat, cook the breakfast sausage until it is no longer pink. Break it up as it cooks. Drain the excess fat.

Combine Base Ingredients: In a large mixing bowl, combine the frozen tater tots, cooked sausage, shredded cheddar, and mozzarella cheese. Stir to evenly distribute.

Fill Baking Dish: Pour the tater tot mixture into the prepared baking dish, spreading it evenly.

Whisk Egg Mixture: In another bowl, whisk together the eggs, milk, salt, pepper, garlic powder, and onion powder until smooth.

Add Egg Mixture: Pour the egg mixture evenly over the tater tot and sausage mixture in the baking dish.

Bake: Bake uncovered in the preheated oven for 60 to 70 minutes, or until the eggs are fully set and the top is golden brown.

Optional: If preparing ahead, cover the unbaked casserole and refrigerate. When ready to bake, remove from fridge and bake as directed (may need a few extra minutes).