Preheat the oven to 375°F and lightly grease a baking dish.
Cook the sausage in a skillet over medium heat until browned, breaking it apart as it cooks. Drain excess grease and set aside.
Prepare the eggs by either lightly scrambling them or whisking them with milk, salt, pepper, chili powder, and cumin.
Assemble the casserole by spreading salsa on the bottom of the dish, followed by sausage, tortillas, egg mixture, and cheese.
Bake uncovered for 25–35 minutes, until the center is set and the top is lightly golden.
Rest for 5–10 minutes, then slice and serve with optional toppings.