Preheat and prep: Heat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with cooking spray or butter.
Cook the sausage: Warm a large skillet over medium heat. Add the sausage, breaking it up with a spoon, and cook until browned and cooked through, about 6–8 minutes.
Drain excess fat if needed.
Sauté aromatics: Add the chopped onion and bell pepper to the skillet with the sausage. Cook 3–4 minutes until softened. Stir in the garlic for the last 30 seconds.
Remove from heat.
Whisk the custard: In a large bowl, whisk together the eggs, milk or half-and-half, salt, pepper, and paprika until smooth.
Assemble the base: Spread the sausage and veggie mixture evenly in the baking dish. Sprinkle 1 1/2 cups of the shredded cheese over the top.
Add tater tots: Arrange the frozen tater tots in a single, snug layer on top of the cheese. Neat rows help them crisp more evenly.
Pour and finish: Slowly pour the egg mixture evenly over the tots, tilting the pan gently so it settles throughout.
Top with the remaining 1/2 cup cheese.
Bake: Place the dish on the center rack and bake 40–50 minutes, until the eggs are set in the middle and the tots are golden and crisp. If the top browns too quickly, tent loosely with foil for the last 10 minutes.
Rest and serve: Let the casserole rest for 10 minutes before slicing. Add toppings like chives, salsa, or hot sauce if you like.