1. Preheat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish with cooking spray or butter.

2. Spread the frozen shredded hash browns evenly over the bottom of the prepared baking dish, breaking up any clumps.

3. In a large skillet over medium-high heat, cook the breakfast sausage, breaking it into crumbles, until browned and cooked through. Drain off excess grease if needed.

4. Add the diced onion, red bell pepper, and green bell pepper to the skillet with the sausage. Sauté for 5–7 minutes, until the vegetables are softened and lightly golden.

5. Spoon the sausage and vegetable mixture evenly over the layer of hash browns in the baking dish.

6. Sprinkle the drained diced green chiles and sliced black olives evenly over the sausage layer.

7. In a large mixing bowl, whisk together the eggs, whole milk, chili powder, ground cumin, kosher salt, and black pepper until smooth and slightly frothy.

8. Stir half of the shredded cheddar cheese into the egg mixture.

9. Slowly pour the egg and cheese mixture over the layers in the baking dish, tilting the pan gently so it spreads evenly and reaches the corners.

10. Sprinkle the remaining cheddar cheese evenly over the top of the casserole.

11. If making ahead, cover the dish tightly and refrigerate for up to 12 hours. When ready to bake, uncover and let it sit at room temperature while the oven preheats.

12. Bake the casserole uncovered for 40–45 minutes, or until the center is set, the edges are puffed, and the top is golden and bubbly.

13. Remove from the oven and let the casserole rest for 10 minutes to firm up for easier slicing.

14. Sprinkle sliced green onions over the top just before serving, then cut into squares and serve warm.