Sauce: Saute onions in butter or margarine in small saucepan until tender. Add remaining ingredients, simmer 15 minutes, uncovered. Filling: Combine the chopped chicken, sour cream and cheese. Use about 1.5 tablespoons for each crepe. To fill the crepes, place them flat and in the middle of the crepe, place the filling in a line across the crepe. Roll up the crepe jelly roll style and place open edge down in a 9 x 33 cm baking dish. Bake the filled crepes in a 350 degrees oven for about 20 minutes or until hot and bubbly. The crepes can be filled and baked immediately or filled and frozen. Defrost the filled crepes slightly and bake as directed adding a few minutes. To serve, spoon the hot sauce over the crepes and garnish with a slice of avocado or a sprinkle of green onion and a spoon of sour cream.