Heat oven to 375°. In 10-inch skillet, cook zucchini and onions in butter until tender, about 10 minutes. Stir in parsley and seasonings. In a large bowl, blend eggs and cheese. Stir this into vegetable mixture. Separate crescent roll dough and place the triangle-shaped pieces into an 11-inch quiche pan. Or use a 12 x 8-inch baking dish and unroll segments side by side. Press over bottom and up sides to form a crust. Spread crust with mustard. Pour vegetable mixture evenly over crust. Bake for 18 to 20 minutes, or until knife comes out clean. Let stand 10 minutes before serving. To reheat, cover loosely with foil. Heat at 375° for 12 to 15 minutes.