Preheat your oven to 350°F (175°C).
In a large mixing bowl, whisk together the eggs and milk until well combined.
Stir in salt, pepper, and garlic powder.
Add the diced bread to the egg mixture and let it soak for about 10 minutes.
Grease a 9x13-inch baking dish with cooking spray.
Layer the diced ham or sausage evenly in the bottom of the dish.
Sprinkle the diced bell peppers and green onions over the meat.
Pour the soaked bread and egg mixture over the layered ingredients.
Top with grated cheddar cheese, spreading it evenly.
Bake in the preheated oven for 40-45 minutes, or until the top is golden and the eggs are set.