Separate crescent dough into eight triangles and place in a greased 9 in. deep-dish pie plate with points toward the center. Press dough onto the bottom and up the sides of the plate to form a crust; seal seams. Spread with mustard.
In a large skillet, sauté zucchini and onion in butter until tender. In a large bowl, combine the eggs, cheeses, seasonings and zucchini mixture. Pour into crust.
Bake at 375° for 20- 25 minutes or until knife inserted in the center comes out clean. Cover edges loosely with foil if crust browns too quickly.