In a skillet, cook the sausage and onions over medium heat until sausage is crumbled and cooked through.
In a medium mixing bowl, whisk the eggs, milk, sour cream, salt, and pepper. It will be thick.
Grease a 9x13 baking dish and place frozen tater tots in a single layer across the bottom of the pan. Top with the sausage and onion mixture.
Next, sprinkle the diced bell peppers followed by the cheese. Pour the egg mixture evenly over the top. Cover with foil and place in fridge overnight.
When ready to bake, remove casserole from fridge and preheat oven to 350 degrees. Bake covered for 45 minutes and then bake uncovered for 20 minutes until set in the middle, golden, and bubbly.
Enjoy! Serve with sour cream, salsa, and avocado and any other toppings you desire. My little kids like it with katchup :)