Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C).
Place bread cubes in a medium bowl and pour melted butter over top. Add zucchini, onion, egg, and garlic salt; mix well.
Transfer the mixture into a 9x13-inch baking dish and top with cheese.
Cover and bake in the preheated oven for 30 minutes. Uncover the dish and bake for another 30 minutes.
