Creating the Spinach Florentine Breakfast Casserole is both simple and rewarding. Follow these easy steps:

1. Preheat Oven: Start by preheating your oven to 350°F (175°C).
2. Sauté Vegetables: In a large skillet, heat olive oil over medium heat. Add chopped onion and sauté until softened (about 5 minutes). Stir in the chopped spinach and cook until wilted, approximately 2-3 minutes. Remove from heat.
3. Whisk Eggs: In a large bowl, whisk together eggs, milk, garlic powder, salt, and black pepper until well combined.
4. Combine Ingredients: Add the sautéed spinach mixture to the egg mixture, stirring to incorporate. Gently fold in the mozzarella and Parmesan cheese.
5. Add Bread: Incorporate the bread cubes into the egg mixture, ensuring they are adequately coated.
6. Prepare Baking Dish: Lightly grease a 9×13-inch baking dish. Pour the mixture into the prepared dish, spreading it evenly.
7. Bake: Place the casserole in the preheated oven and bake for 30-35 minutes or until the center is set and a little golden brown.
8. Cool: After removing the casserole from the oven, let it cool for 5-10 minutes before slicing. This will make serving easier.
9. Serve: Cut into squares and serve hot.

By following these straightforward steps, you'll have an incredible Spinach Florentine Breakfast Casserole ready to delight your family and guests.