Preheat the oven to 350 degrees F. Spray a 9x13-inch casserole dish with cooking spray.
In a skillet set over medium heat, brown the sausage. Remove the cooked sausage to a paper towel-lined plate to drain.
1 pound breakfast sausage
Add the mushrooms, onion, and bell peppers to the skillet and sauté for 2-3 minutes until softened. Set aside to cool slightly.
½ cup mushrooms, ½ cup onion, ½ cup green bell pepper, ½ cup red bell pepper
In a large bowl, combine the eggs, sour cream, cream, salt, garlic powder, and pepper. Whisk until well combined. Fold in 1 cup of cheese.
12 eggs, 1 cup sour cream, 1/4 cup cream, 1 teaspoon kosher salt, ½ teaspoon garlic powder, ½ teaspoon black pepper, 2 cups shredded cheddar cheese
Layer the cooked sausage and vegetables in the casserole dish. Pour the egg mixture over the top, then sprinkle with the remaining cheese.
Pour the mixture into the prepared pan. Bake for 35-40 minutes, until the edges are set and the center is just barely jiggly.
Serve garnished with sliced green onions.