In a large pot over medium heat, brown the ground beef or lamb until fully cooked, breaking it apart as it cooks. Drain excess fat if necessary.
Add the diced onion, garlic, carrots, and celery to the pot. Sauté for about 5-7 minutes until the vegetables are tender.
Pour in the beef broth, and add the frozen peas, Worcestershire sauce, thyme, rosemary, salt, and pepper. Bring the mixture to a boil, then reduce the heat and let it simmer for 15-20 minutes to allow the flavors to meld.
Once the soup is ready, ladle it into bowls and top each serving with a generous scoop of mashed potatoes.
Garnish with chopped fresh parsley before serving.