Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with non-stick spray or butter.

Cook the Sausage: In a skillet, cook the sausage over medium-high heat until browned and crumbled, about 8-10 minutes. Drain and set aside.

Prepare the Egg Mixture: In a large mixing bowl, whisk together the eggs, milk, salt, black pepper, and mustard powder until well combined.

Assemble the Casserole: In the prepared baking dish, layer the cubed bread evenly along the bottom. Sprinkle the cooked sausage on top of the bread, followed by the shredded cheddar cheese. Add the chopped onions and bell peppers evenly over the top.

Pour the Egg Mixture: Slowly pour the egg mixture over the layers in the baking dish, ensuring it covers everything evenly.

Bake: Place the casserole in the preheated oven and bake for 50-60 minutes, or until the eggs are set and the top is golden brown.

Let It Rest: Allow the casserole to cool for about 10 minutes before slicing and serving. Garnish with chopped fresh parsley.