In a shallow bowl, beat egg, water, 1/2 teaspoon salt and pepper. Set aside 2 tablespoons bread crumbs. Place the remaining crumbs in a large resealable plastic bag. Dip chicken in egg mixture, then place in bag and shake to coat.
In a skillet, cook chicken in 2 tablespoons oil for 2-3 minutes on each side or until golden brown; remove and set aside. In the same skillet, saute zucchini in remaining oil until crisp-tender; drain. Transfer to a greased 13-in. x 9-in. x 2-in. baking dish.
Sprinkle the reserved bread crumbs over the zucchini. Top with tomato slices; sprinkle with 2/3 cup mozzarella cheese, basil and remaining salt. Top with chicken. Cover and bake at 400 degrees F for 25 minutes. Uncover; sprinkle with remaining cheese. Bake 10 minutes longer or until cheese is melted.