Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, cook the breakfast sausage until browned. Drain excess grease if necessary and set aside to cool slightly.
In a large mixing bowl, whisk together the eggs, milk, salt, pepper, garlic powder, and onion powder until well combined.
Add in the cubed bread, cooked sausage, shredded cheese, and diced bell peppers and onions (if using). Stir until everything is evenly coated with the egg mixture.
Pour the mixture into a greased 9x13-inch baking dish, spreading it out evenly.
Bake in the preheated oven for about 45 minutes, or until the eggs are set and the top is lightly golden.
Remove from the oven and let it cool for a few minutes before slicing into squares. Serve warm.
This casserole can be prepared the night before. Just cover it with plastic wrap and refrigerate. Remove from the fridge 30 minutes before baking, then bake according to the instructions.
Feel free to customize the ingredients by adding cooked bacon, ham, or any vegetables you enjoy.
Leftovers can be stored in an airtight container in the refrigerator for up to 3 days. Reheat in the oven or microwave before serving.