Heat olive oil in a large pot over medium heat. Add the diced onion, minced garlic, carrots, and celery. Sauté for about 5 minutes until vegetables soften.
Add the ground lamb (or beef) to the pot. Cook until browned, breaking it apart with a wooden spoon, for about 8-10 minutes.
Stir in the tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Mix well and cook for an additional 2 minutes.
Add the cubed potatoes and beef broth to the pot. Bring to a boil, then reduce heat to a simmer. Cover and cook for about 15-20 minutes or until the potatoes are tender.
Add the frozen peas to the soup and stir. Cook for an additional 5 minutes to heat the peas through.
Taste and adjust seasoning if necessary.
Ladle the soup into bowls and garnish with chopped parsley if desired.
For added creaminess, mash some of the potatoes in the soup before serving.