Preheat oven to 350 degrees.

Place ground beef and breadcrumbs in a large bowl.

Mince onion, bell pepper, celery, mushrooms and garlic very finely or pulse in food processor until small, but not puréed. Add minced vegetables, beaten egg, salt and pepper to the ground beef mixture. Mix by hand until combined well.

Place mixture on broiler pan and shape into loaf and bake 30 minutes.

Mix ketchup and water in small bowl while meatloaf is baking. Spoon over loaf and spread to edges. Return meatloaf to oven for additional 30−45 minutes until cooked through or internal temperature registers 155 degrees on meat thermometer. Remove from oven and allow to rest 10 minutes before serving.