In a large skillet cook zucchini and onion in hot butter or margarine about 8 minutes or just until tender, stirring occasionally. Remove from heat. Stir in parsley, salt, pepper, oregano, basil, and garlic powder. In a large bowl, combine eggs and cheese. Stir in zucchini mixture; set aside.
For crust, separate crescent roll dough into triangles; press into bottom and up side of a 10-1/2- or 11-inch quiche dish or a 10-inch pie plate. Spread crust with mustard.
Spoon zucchini mixture into crust, spreading evenly. Bake in a 375 degree F oven for 25 to 30 minutes or until knife inserted in center comes out clean. Let stand 10 minutes; cut into wedges to serve. Makes 6 to 8 servings.