For the meatballs: Preheat the oven to 450 degrees F. In a mixing bowl, combine the beef and pork. Then add the breadcrumbs, parsley, coriander, garlic, paprika, black pepper, allspice, cayenne and egg. Sprinkle with salt. Form into 1 1/2-inch meatballs and arrange on a baking sheet. Spray with olive oil and bake to lightly brown, 10 to 12 minutes.
For the casserole: Bring a medium pot of water to a boil, salt the water and cook the barley to tender, about 20 minutes. Drain.
Meanwhile, melt the butter over medium heat. Add the onions and season with salt and pepper. Cook until golden in color and sweet, stirring frequently, 15 to 20 minutes.
In a casserole, combine the barley, onions and sauerkraut. Top with the Swiss cheese and arrange the meatballs in the casserole. Cool and cover for a make-ahead meal.
Combine the sour cream with the ketchup and relish. Season with salt and pepper and store in a plastic food storage bag.
Bring the casserole to room temp. Preheat the oven to 350 degrees F and bake until the cheese is melted and the casserole is hot throughout. Cut the corner of the baggie, drizzle the dressing over the casserole and serve.