Place the lamb and beef stew meat in the bottom of the slow cooker.
Add the potatoes, carrots, parsnips, onion, and garlic on top of the meat.
Stir the tomato paste into the beef broth until smooth, then pour the mixture over the vegetables and meat.
Sprinkle in the thyme, rosemary, salt, and pepper. Add the bay leaves.
Cover and cook on low for 8 hours, until the meat is fork-tender.
Remove the bay leaves. Ladle the stew into bowls and sprinkle with fresh parsley before serving.