Begin by preheating your oven to 350°F (175°C). Prepare a 9x13-inch baking dish by greasing it with cooking spray or a thin layer of butter to prevent sticking.
In a large mixing bowl, crack in the eggs and pour in the whole milk. Whisk them together thoroughly until the mixture is smooth and well combined. Add the garlic powder, paprika, salt, and black pepper, continuing to whisk until the seasonings are evenly distributed.
Evenly spread the cubed bread across the bottom of the prepared baking dish, creating a solid layer.
Carefully pour the egg mixture over the bread cubes, ensuring it seeps through to coat all the pieces evenly.
Layer the crumbled sausage, diced bell pepper, and chopped onion over the egg-soaked bread, distributing them generously across the dish.
Finish by topping the mixture with the shredded cheddar cheese, ensuring an even coverage to achieve a deliciously cheesy topping.
Cover the baking dish with aluminum foil, which helps to retain moisture, and place it in the preheated oven. Bake for 30 minutes.
After the initial baking time, carefully remove the foil and return the dish to the oven. Bake for an additional 15-20 minutes, or until the cheese is bubbly and golden, and a knife inserted into the center comes out clean.
Once baked to perfection, remove the casserole from the oven and allow it to rest for about 5 minutes. This will help it set before slicing.
Just before serving, garnish with freshly chopped green onions for a pop of color and flavor. Cut into squares and serve warm.
Notes
For a lighter option, substitute the breakfast sausage with turkey sausage.