Heat olive oil in a large skillet or saute pan. Add onions, and saute over medium heat for 10-15 minutes. Add salt, lower heat, and cook for 10 minutes. Add white wine, turn heat back up to medium, and simmer uncovered for 15 minutes. Start boiling water for pasta. Add chopped greens to onion sauce, stir and cook for about 5 minutes. Stir in crumbled cheese, and turn heat to low while pasta cooks. After cooked pasta is drained add it to the sauce, and stir briefly in pan before serving. Sprinkle with walnuts and parmasean, and serve.