In a mixing bowl, combine the ground beef, ground pork, breadcrumbs, grated Parmesan cheese, parsley, eggs, chopped onion, garlic powder, salt, and black pepper. Mix until all ingredients are combined evenly.
Shape the mixture into meatballs, about 1 inch in diameter. You should have approximately 24 meatballs.
If desired, you can brown the meatballs on a baking sheet in the oven at 400°F (200°C) for 15 minutes, but this step is optional.
In the crockpot, combine the beef broth, Worcestershire sauce, and dried thyme. Stir to mix.
Carefully place the meatballs into the crockpot, ensuring they are submerged in the broth mixture.
Cover and cook on low for 4 hours, or until the meatballs are cooked through and tender.
About 10 minutes before serving, sprinkle the shredded Swiss cheese on top of the meatballs in the crockpot and cover to allow the cheese to melt.
Serve hot, garnished with additional parsley if desired.