Preheat oven to 375. Prepare a 2-quart casserole dish with cooking spray; set aside. To prepare filling, combine soup, 1 1/4 cups milk, salt, turkey, vegetables, and cheddar cheese in a mixing bowl. Pour into prepared dish. Bake, uncovered for 15 minutes. Meanwhile, to prepare lattice, combine baking mix, remainig milk, and egg whites in another mixing bowl. Mix until soft dough forms. Stir casserole and spoon dough over hot turkey mixture to form lattice design. Bake, uncovered again, for 25 minutes or until lattice is golden brown.