Lightly brown meat in a large skillet. Add salt and onion and cook about 5 minutes. Add tomato sauce, water and oregano. In another pan, cook noodles until al-dente; drain, add to beef mixture. Combine sour cream and ricotta cheese. In a 9x13-inch casserole dish, layer half of the noodle mixture, add the spinach in a layer and dollop 1/2 of the sour cream mixture. Top with remainder of noodles and rest of sour cream mixture. Sprinkle with Parmesan cheese. Bake at 375^ for 30-40 minutes.