A delicious and easy casserole that can be made the night before and reheated in the morning for a quick breakfast treat. Use frozen O'Brien potatoes to make it even easier.
Preheat oven to 350°F. Butter a 9x13-inch baking dish and set aside.
Cook sausage in a large, heavy skillet over medium-high heat until browned, about 5 minutes. Using a slotted spoon, transfer cooked sausage to a paper towel-lined plate.
Remove all but 1 tbsp of the fat in the skillet. Add onion, bell peppers, and chiles and cook about 3 minutes until onion and peppers have softened. Mix in flour, oregano, and cumin and cook for 1 minute, stirring occasionally. Stir in milk. Cook until mixture thickens and comes to just under a boil, stirring occasionally, about 5 minutes. Season to taste with salt and pepper. Remove from the heat. Stir the cooked sausage and 1 cup of the cheese into the sauce.
Spread the potatoes in the prepared baking dish and top with the sausage mixture. Sprinkle the top with the remaining 1/4 cup cheese.
At this point you can cover and refrigerate overnight if desired.
Bake, covered, until the potatoes are tender, about 45 minutes or until the casserole is bubbling around the edges and cooked through. Remove from the oven and let sit for about 10 minutes before scooping out servings. Sprinkle the tops with green onions and cilantro.
For a dairy-free version, use a plant-based milk and leave off the sour cream and cheese.