Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter. This helps keep the casserole from sticking and makes cleanup easier.
Cook the sausage. Place the breakfast sausage in a skillet over medium heat.
Break it up with a spoon and cook until it is browned and fully done, then drain off any extra grease.
Mix the egg base. In a large bowl, whisk together the eggs, milk, salt, pepper, garlic powder, and onion powder. Stir until everything looks smooth and well blended.
Assemble the casserole. Spread the cooked sausage evenly in the bottom of the baking dish. Sprinkle the shredded cheese over the sausage, then pour the egg mixture on top.
Arrange the frozen tater tots in a single layer over everything.
Bake until golden and set. Bake uncovered for 40 to 50 minutes, or until the eggs are set and the tater tots are crisp and golden brown. If the top starts browning too fast, you can loosely cover it with foil during the last part of baking.
Let it rest before serving. Take the casserole out of the oven and let it sit for 5 to 10 minutes. This helps it settle so you can cut cleaner squares and serve it more easily.
Add toppings if you want. Sprinkle chopped green onions over the top for a fresh finish.
You can also serve it with salsa, sour cream, or a little extra cheese.