Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius).
In a skillet over medium heat, cook the breakfast sausage until browned, breaking it into pieces as it cooks. Drain excess grease and set aside.
In a large mixing bowl, whisk together the eggs, milk, salt, pepper, garlic powder, and oregano until well combined.
Add the cooked sausage, diced bell peppers, diced onions, and bread cubes to the egg mixture. Gently fold all ingredients together until the bread is well-coated.
Grease the 9x13-inch baking dish with cooking spray or butter.
Pour the breakfast casserole mixture into the prepared dish, spreading it evenly.
Top with shredded cheddar cheese.
Bake in the preheated oven for 40-45 minutes or until the casserole is set in the center and the top is golden brown.
Let it cool for a few minutes before slicing. Garnish with fresh parsley, if desired.