01 -
Grease a 9x13-inch baking dish with butter or cooking spray.
02 -
Spread cubed bread evenly in the bottom of the dish.
03 -
In a skillet, heat olive oil over medium heat. Sauté onions until soft, then add spinach and cook until wilted.
04 -
Distribute the spinach and onion mixture over the bread. Sprinkle with shredded cheese.
05 -
In a bowl, whisk together eggs, milk, garlic powder, salt, and pepper.
06 -
Pour egg mixture evenly over the bread, pressing down slightly to help it soak in.
07 -
Cover tightly with foil or plastic wrap and refrigerate overnight (or at least 6 hours).
08 -
In the morning, preheat oven to 350°F (175°C).
09 -
Bake uncovered for 45–55 minutes, until golden and the center is set.
10 -
Let cool for 10 minutes before slicing and serving.