Preheat the oven to 350°F (175°C).
In a large mixing bowl, whisk together the eggs and whole milk until fully combined.
Add in the salt, black pepper, garlic powder, and onion powder, and mix well.
In the greased baking dish, spread the cubed bread evenly on the bottom.
Sprinkle the cooked sausage, chopped spinach, diced bell pepper, and cheddar cheese over the bread cubes.
Pour the egg mixture over the entire dish, ensuring it is evenly distributed.
Press down gently on the top to help the bread absorb the egg mixture.
Cover the dish with foil and let it sit for at least 30 minutes or refrigerate overnight for improved flavors.
Bake covered for 30 minutes, then remove the foil and bake for an additional 15 minutes, or until the top is golden brown and a knife inserted comes out clean.
Let it cool for a few minutes before slicing. Garnish with fresh herbs if desired.