Combine the ground beef with shredded zucchini, onion, mushrooms, garlic powder, egg, breadcrumbs, salt, and pepper.
Mix lightly with hands until thoroughly blended.
Pack the meat mixture into a lightly greased 9-by-5-by-3-inch loaf pan.
Bake for 1 hour.
About 15 minutes before the meatloaf is done, carefully pour off excess fat. I place a plate or lid over the pan and drain it into a jar or cup to be discarded in the trash later.
Top with ketchup and return to the oven and continue baking for 10 to 15 minutes.