Prepare the crumble topping. Combine all dry ingredients in a medium bowl (flour, oats, sugar, spices, salt, nuts/seeds) then pour melted coconut oil or vegan butter and stir to combine. If too dry, add a bit more butter or oil until you get a crumble texture.
Layer cubed apples on an oven dish, add lemon juice and sprinkle cornstarch or arrowroot powder on top. Mix to combine.
Top the apple base with the crumble, distributing evenly.
Cook at 190°C / 375°F for 35-40 minutes, or until the crumble turns golden. Enjoy as is, or topped with vegan whipped cream or ice cream!