Preheat the oven to 350°F.
In a large skillet over medium heat, cook the breakfast sausage until browned, breaking it apart as it cooks.
Add the diced onion and bell pepper, cooking until softened, about 5 minutes.
In a large mixing bowl, whisk together the eggs, milk, salt, black pepper, garlic powder, and oregano.
Stir in the cooked sausage mixture and cubed bread until well combined.
Pour the mixture into a greased 9x13-inch baking dish.
Sprinkle the shredded cheddar cheese evenly over the top.
Bake in the preheated oven for 30-35 minutes, or until the casserole is set in the center and the cheese is golden brown.
Allow to cool for 5-10 minutes before slicing and serving.