In a large bowl, combine the diced bell peppers, onions, diced tomatoes, chopped spinach, and cubed bread. Stir gently to ensure the bread is distributed evenly among the vegetables.

In a separate bowl, beat the eggs with the milk, salt, black pepper, garlic powder, and onion powder until the mixture is smooth and slightly frothy.

Pour the egg mixture evenly over the vegetable and bread mix. Stir gently so that all the bread cubes soak up the liquid. Use a spatula to press down lightly to encourage absorption.

Fold in the shredded cheese, saving a bit to sprinkle on the top for a beautiful, cheesy crust.

Cover the bowl with plastic wrap and refrigerate overnight, letting the flavors meld for at least 6 to 12 hours.

The next day, preheat your oven to 350°F (175°C). Transfer the mixture to a greased baking dish, discarding the plastic wrap.

Bake for 30 to 35 minutes, until the center is set and the top is golden brown. Check with a toothpick; it should come out mostly clean.

Allow the casserole to rest for 5 to 10 minutes before slicing, ensuring cleaner pieces.