Preheat oven to 350.
Pulse the bread in food processor to make crumbs. Toss with melted butter and set aside.
Peel and slice apples. In large bowl, toss apples with sugars, cinnamon, salt, apple cider (or juice or water), lemon zest and juice (if using), and vanilla.
In 8-x-8 square baking dish or a deep-dish pie dish, layer half the apple mixture (including juices), then cover with half the bread crumbs. Top with remaining apple mixture and remaining crumbs.
Bake for 50 minutes to 1 hour, until topping is golden brown and apples are bubbling.