In a large frying pan, sauté onion until golden. Add mushrooms and sauté until beginning to soften. Add remaining vegetables and continue to sauté, stirring often, until mixture is soft. Stir in salt, pepper, and onion soup mix. Set aside to cool.

Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Roll out dough to a rectangle, approximately 10×16 inches (25×40 centimeters). Spoon filling over dough and spread out over surface. Carefully begin to roll dough in the length, pinching two ends together along the way so that the filling does not escape.

Using a large spatula, transfer strudel to Gefen Parchment Paper-lined baking sheet. Brush with beaten egg and sprinkle with sesame seeds. Bake for 35 minutes, or until dough turns a golden brown.