In a large bowl, combine the flour, salt and onion powder; cut in shortening until crumbly. Gradually add water, tossing with a fork until dough forms a ball. Divide dough in half. Line a 9-in. pie plate with bottom crust; trim pastry even with edge.
In a large skillet, saute peppers and onion in 1 tablespoon oil. Add the beef, soup, mushrooms, Worcestershire sauce, garlic powder and pepper. Bring to a boil. Combine cornstarch and water until smooth; stir into skillet. Bring to a boil; cook and stir for 2 minutes or until thickened. Cool.
Spoon into crust. Top with potatoes. Brush remaining oil over potatoes. Roll out remaining pastry to fit top of pie; place over filling. Trim, seal and flute edges. Cut slits in pastry. Brush with egg.
Bake at 375° for 45 minutes. Cover edges loosely with foil. Bake 10 minutes longer or until golden brown.