Preheat the oven to 350 degrees F. Grease a 9-inch x 13-inch baking dish with nonstick spray. Set aside.
Place a large non-stick skillet over medium-high heat. Add the bacon and cook for 3 minutes, stirring occasionally. Add the diced onion to the bacon. Continue to cook for another 5 minutes or until the bacon is cooked and the onions are translucent. Use this cooking time to prep your other ingredients.
Transfer the bacon, onions, and any grease in the skillet to a large mixing bowl. Stir the bell peppers, green onions, 2 cups of cheese, and chopped sausage in with the bacon and onions.
Add the tater tots to the meats and veggies and mix everything together. Pour the mixture into the prepared casserole dish. Set aside.
In a medium mixing bowl, whisk together the eggs, milk, garlic powder, pepper, and salt. Pour the egg mixture over the top of the tater tot mixture.
Bake for 40 to 45 minutes. Remove the dish from the oven and sprinkle with the remaining 1/2 cup of shredded cheese. Bake for another 5 minutes or until the cheese is melted.
Remove from the oven and let rest for 5 minutes. Sprinkle the casserole with green onions, and then cut it into portions and serve warm.