Start by frying chopped onion in skillet until golden brown and set aside.
Take a large, wide stockpot, and place sliced onion, cut up carrots and parsnips on bottom. Place fish trimmings over vegetables. Pour 1/2 of the browned, fried onions on top. Season with salt and pepper. Fill pot 2/3 full of water, and set to boil. Lower heat. Add parsley to simmering broth.
In a large mixing bowl, combine ground fish with ground onions, salt and pepper, remaining fried onion, eggs, and matza meal. Knead dough using hands until ingredients are well incorporated. With wet hands, shape gefilte fish into oblong balls, and drop into simmering stock. Cook 3 hours covered over low heat. Towards the end, sprinkle surface with cold water. Makes at least 30 generous-sized gefilte fish.