Heat a large stock pot over medium-high heat. Spray with non-stick cooking spray or a little oil if you're not using a non-stick pan.
Add diced onion and garlic to the pan along with a pinch of salt and pepper. Sauté until onions start to soften, about 4-6 minutes. Place ground lamb in the pan along with another pinch salt and pepper then begin breaking down in to bite-sized pieces with a potato masher or wooden spoon.
Once lamb is about halfway browned, add in the carrots and celery plus another pinch salt and pepper. Cook until veggies start to become tender, about 6-8 minutes. Stir in Worcestershire, oregano, and potato cubes. Cook for 1-2 more minutes, stirring occasionally.
Pour beef broth and tomato into the pan and bring to a boil. Stir in frozen vegetables then bring back to a boil. Cover pot with a lid then reduce heat to low and simmer for 30 minutes. Add fresh parsley then check once more for seasoning. Adjust accordingly before serving.
Notes
This dish works great with ground beef if you prefer. It's also great for freezing.