Cook the Italian sausage in a skillet over medium heat, breaking it into crumbles until browned (6-8 minutes). Drain excess fat.

Grease a 9x13-inch baking dish with butter or cooking spray.

Layer half of the cubed Italian bread in the dish. Add half of the cooked sausage, then layer with chopped tomatoes, spinach, and cheese. Repeat.

Whisk together eggs, milk, Italian seasoning, garlic powder, salt, and pepper until frothy (2-3 minutes).

Pour the custard mixture over the layers and press down gently to ensure absorption.

Cover with plastic wrap and refrigerate overnight.

Preheat the oven to 350°F (175°C) and bake for 45-55 minutes until golden brown.

Let cool for 10 minutes before slicing and serving.