Preheat the oven to 400F.
Lightly grease a 9X13 baking dish
Line the bottom with hash browns to make the base
Bake in the oven until lightly browned, approximately 20 mins or until slightly dried.Molly's note:[This is the secret to get the potatoes just right and for the casserole to hold together when cut into squares.] Heat a skillet over medium-high heat.
Add red pepper, onion, and sausage and cook until the sausage is no longer pink and the vegetables are softened.
Add spinach and cook for another 2 minutes until spinach is wilted. Set aside and let cool slightly.
Preheat the oven to 350F. (Lower from 400F)
In a large mixing bowl, combine the remaining ingredients (leaving 1/2 cup cheese and the green onions for topping) with the sausage and vegetables and mix until well combined.
Pour into the prepared baking dish and top with the remaining 1/2 cup cheddar cheese and green onions.
Bake at 350F for 30 minutes or until the eggs are completely set.
Let cool for 5 minutes before serving.