In soup pot, cook sausage pieces, using some olive oil, as needed. Set aside cooked sausage. In same soup pot, heat 2 tablespoons of olive oil. Cook cabbage for about five minutes. Add onion and mushrooms. Stir mixture, and cook for about five more minutes. Add chicken or vegetable stock and can of diced tomatoes, along with the liquid. Bring to gentle boil. Add potatoes. Lower heat, and cook soup until potatoes are soft. Add sausage. Season with salt and pepper to taste. Garnish with fresh Parsley.