Rinse the veal and pat dry. Place into a 13x9x2-inch baking dish.

Heat margarine in large skillet, add onion, and cook five minutes. Add celery and mushrooms. Sauté until soft, about 10 minutes.

Place spinach in medium bowl. add bread crumbs, egg, parsley, salt and ground black pepper to the spinach; mix well to combine. add the onion mixture to spinach; mix well.

Open the pocket and fill the cavity with stuffing, pressing to fit. Place stuffing mostly in the center of the pocket. Close the pocket with wooden toothpicks or leave as is. Brush veal generously with olive oil. Season with salt, pepper, garlic powder, onion powder, and paprika.

Preheat oven to 350 degrees Fahrenheit.

Prepare the sauce first. Whisk together ketchup, water, brown sugar, soy sauce, white vinegar, celery salt, ground black pepper and onion powder. Pour over meat.

Cover pan, and bake until tender and juices run clear, about 2 hours. Slice when cool.