Preheat the oven to 400°F.
In a large bowl, combine the ground beef, ground lamb, breadcrumbs, parsley, Parmesan cheese, egg, garlic, salt, pepper, and Worcestershire sauce. Mix until well combined.
Form the mixture into meatballs, about 1 inch in diameter.
Heat olive oil in a large oven-safe pot over medium heat. Add the meatballs and brown on all sides, about 5 minutes. Remove the meatballs and set aside.
In the same pot, add the onion, carrots, and potatoes. Sauté for about 5 minutes until the vegetables begin to soften.
Stir in the beef broth, tomato paste, thyme, and rosemary. Bring to a simmer.
Return the meatballs to the pot, cover, and transfer to the oven. Bake for 30 minutes.
Remove from the oven, stir in the frozen peas, and let sit for 5 minutes before serving.