Preheat the oven to 350F. Using a medium-size bowl, mix together the bread cubes with the melted butter.
Mix in the zucchini, chopped onion, and garlic salt
Add the beaten egg and mix it in with all the other ingredients
Place the zucchini mixture in a greased casserole dish
Top with the shredded Cheddar cheese and cover with aluminum foil. Bake for 30 mins covered, then remove the foil and bake for another 30 mins.