Preheat the oven to 375°F (190°C). Lightly grease a 9-inch pie dish or a baking pan.

Cook the sausage: In a medium skillet, cook the sausage over medium heat until browned and fully cooked through. Break it into crumbles using a spatula as it cooks.

Sauté vegetables: In the same skillet, sauté the chopped onion (and bell pepper, if using) until softened, about 4-5 minutes. Set them aside to cool slightly.

Prepare the batter: In a large mixing bowl, whisk together the eggs, half-and-half (or milk and cream mixture), flour, baking powder, salt, and black pepper until smooth and well-combined.

Layer the ingredients: In the prepared pie dish, layer the cooked sausage and sautéed vegetables evenly across the bottom. Sprinkle the shredded Monterey Jack and cheddar cheeses over the sausage.

Pour the batter: Slowly pour the egg mixture over the sausage and cheese, ensuring it spreads evenly throughout the pie dish.

Bake: Place the pie in the oven and bake for 35-40 minutes, or until the center is set and the top is golden brown.

Cool and garnish: Let the pie cool for about 5 minutes before slicing. Garnish with chopped green onions or chives if desired.

Serve: Slice and serve the pie warm. This dish pairs well with a simple side salad or fresh fruit for a well-rounded meal.