While apple mixture is baking, combine flour, cinnamon, brown sugar, oats, and lemon zest in medium bowl. Cut in butter until crumbly. Sprinkle on top of apples and return to oven.
4 Reduce heat to 375 degrees and bake 30-35 minutes or until apples are tender and topping is golden. If topping browns too quickly, cover loosely with aluminum foil to prevent excess browning.