Preheat the oven to 200ºC . Saute the onions in 2 tablespoons of the butter or vegan margarine for 10 minutes, until soft but not browned. In another pan, heat 4 tablespoons of the butter or vegan margarine and saute the crumbs until crisp. Melt the remaining butter or vegan margarine in a small saucepan. Spread one phyllo pastry sheet out on a large board and brush with butter or margarine. Put another pastry sheet on top and brush with more butter or margarine. Repeat until all sheets have been used. Spread the onions evenly on top of the pastry, keeping the edges clear. Put the asparagus over the top of the onions and sprinkle with three-quarters of the crumbs and the parsley. Fold over 5 cm all around the pastry, then fold the long edges over to make a roll. Place the roll, seam side down, on a baking sheet and bend it around into a horseshoe shape. Brush with remaining melted butter or margarine and sprinkle with the remaining crumbs. Bake for 40 minutes, until golden and crisp. Garnish with parsley sprigs, lemon slices and asparagus tips. Combine Yogurt and Herb Dressing ingredients, and serve with Strudel.