Cook Sausage* Brown and crumble the sausage in a pan.
Cook Vegetables* Sauté onions and bell peppers (if using) in the same pan until soft.
Assemble* Place the cooked sausage in a greased pie dish, add the cooked vegetables and grated cheeses on top.
Prepare Egg Mixture* Mix eggs, milk, flour, baking powder, salt, and pepper.
Combine* Pour the egg mixture over the sausage, vegetables, and cheese in the pie dish.
Bake* Cook in a preheated oven at 350°F (175°C) for 35-40 minutes until firm.
Serve* Let the pie cool slightly before serving, and garnish with green onions or chives if desired.