Preheat your oven to 350°F (175°C).
Prepare the Filling: In a large mixing bowl, combine the sliced apples, cinnamon, maple syrup, lemon juice, plant-based milk or water, vanilla extract, corn starch (or arrowroot powder), and a dash of salt. Mix well until the apples are evenly coated. Transfer the apple mixture to a baking dish (around 9x9-inch or similar size).
Prepare the Crumble Topping: In another mixing bowl, combine the rolled oats, almond flour, cinnamon, and salt. Add the unsweetened applesauce maple syrup and mix until the mixture forms clumps. Stir in the chopped nuts if using, mixing until evenly distributed.
Assemble the Apple Crisp: Sprinkle the crumble topping evenly over the apple mixture in the baking dish, gently pressing it down to form a crust.
Bake in the preheated oven for 45-55 minutes or until the topping is golden, the filling is bubbly, and the apples are tender (test the apples with a fork).
Cool and Serve: Remove the apple crisp from the oven and let it cool for 10-15 minutes. Serve optionally with a scoop of vegan ice cream and some homemade caramel sauce, maple or date syrup.
Enjoy your delicious and healthy vegan apple crisp!