Preheat oven to 475 degrees. Line pie shell with foil; fill with pie weights (or dried beans or rice). Bake 8 minutes. Remove from oven; carefully remove foil and pie weights and return to oven to bake 4 more minutes. Set aside. Reduce oven temperature to 375 degrees.
Brown ground beef in large skillet; drain off extra grease. Add zucchini, onions and mushrooms. Cook, stirring occasionally until veggies are tender. Stir in flour; cook 2 minutes, stirring constantly. Remove from heat.
In medium bowl, combine eggs, milk, cheese and seasonings. Stir into ground beef mixture; pour into crust. Bake 35 minutes or until knife inserted near center comes out clean.