In a large skillet, saute the zucchini, onion and garlic in butter until tender; set aside. In a large bowl, whisk the eggs, Parmesan cheese, parsley, basil, marjoram and salt. Stir in zucchini mixture and Monterey Jack cheese.
Pour into a greased 1-qt. baking dish.
Bake at 350° for 20-25 minutes or until a knife inserted near the center comes out clean.