Prepare cream sauce and set aside. Melt 2 tablespoons butter in heavy skillet and saute mushrooms and scallions over high heat, stirring constantly. Add dill, cottage cheese, and sour cream, and stir together until cheese melts. Add ¾ cup cream sauce and lemon juice, and cook until mixture thickens slightly. Add about a tablespoon of fresh parsley. Set mixture aside and keep warm. In ovenproof iron skillet, melt remaining 2 tablespoons butter. Beat eggs and ½ cup cream sauce together, and pour into pan. Do not stir. Keep eggs on burner for a couple of minutes, until bottom begins to set, then put into preheated 400 degree F oven and bake until puffed and golden brown. Remove from oven and place mushroom mixture on half of omelet. Arrange avocado slices on top and fold omelet, then transfer to a platter if desired. Thin remaining cream sauce with white wine and pour over omelet. Garnish with chopped parsley.