Brown beef in a large saucepan of cast iron skillet over medium high heat, about 5 min. Add celery, leek and mushroom and cook another 5-8 min, or until veggies are tender. Add beef broth, red wine and salt. Bring to a boil, then reduce heat and simmer for 10-15 min. While beef mixture is cooking, saute sweet potato noodles for 2-3 min in olive oil over medium heat. Add 2 tbsp water to help steam and cook another minute or until noodles start to soften, but retain their crunch (like an al dente noodle).
Right before serving, remove beef mixture from heat and stir in yogurt. Serve warm topped with fresh chopped parsley.