Preheat your oven to 400°F (200°C). Spray a 9 x 13-inch baking dish with cooking spray.

In a large skillet over medium-high heat, cook the breakfast sausage until no longer pink, about 5-7 minutes. Add green pepper, red pepper, onion, and minced garlic and sauté for an additional 5 minutes.

Layer half of the thawed hash browns evenly across the bottom of the prepared baking dish.

Sprinkle half of the sausage mixture over the hash browns and top with 1 cup of shredded cheddar cheese.

Add the remaining hash browns on top of the cheese, spread the rest of the sausage and vegetable mixture, and finish with the remaining cheese.

Whisk together eggs with milk, salt, pepper, and red pepper flakes until pale yellow. Pour the egg mixture evenly over the layered ingredients.

Bake for approximately 35-40 minutes, until the eggs are fully set and the top is golden brown.

Let cool for a few minutes, then sprinkle chopped green onions on top before serving.