Cook spaghetti according to package directions until al dente. Drain and place spaghetti in a greased 1.5 quart casserole dish. (I just spray with nonstick cooking spray.) Melt butter in medium saucepan over low heat. Remove from heat, and stir in sour cream, lemon peel, and lemon juice. Mix until smooth. Pour mixture over spaghetti in casserole dish. Mix well. Top with freshly grated parmesan. Bake in a preheated 400 degree oven for 15 minutes, or until heated through. Remove from oven, and add parsley. Season with salt and freshly ground pepper to taste. Serve immediately.