Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish.

In a skillet, cook the sausage over medium heat, breaking it up until browned and cooked through, about 6 to 8 minutes. Drain excess fat.

In a medium bowl, whisk together the eggs and milk until smooth. Season with salt and pepper.

Spread the cooked sausage in the prepared dish, followed by an even layer of bread cubes and then the diced vegetables if using.

Pour the egg mixture over the layers, ensuring it soaks into the bread.

Sprinkle the cheese on top.

Bake in the preheated oven for 30 to 35 minutes, until the center is set and lightly golden on top.

Let the casserole rest for 5 to 10 minutes before slicing and serving.