Brown sausage and onions. Add tomato paste and water. Stir until combined, then simmer for 5 minutes over medium heat.
Cook noodles according to package instructions. Drain and pour into a lightly greased 13" x 9" casserole dish. Spread sausage and tomato mixture on top. Mix together the sour cream, cream cheese and soup, then pour over meat. Sprinkle with cheese.
Bake for 30 minutes. Garnish with chopped parsley. Serve immediately. Store covered in refrigerator for up to 5 days.