Preheat the oven to 350°F (175°C). Lightly grease a 9x9-inch baking dish or similar-size casserole.

Prepare the apples: In a large bowl, combine sliced apples, lemon juice, sugar, cinnamon, nutmeg, vanilla, cornstarch, and a pinch of salt. Toss well until the slices look evenly coated and glossy.

Make the crumble topping: In another bowl, stir together oats, flour, nuts (if using), sugar, cinnamon, and salt. Pour in the melted coconut oil or vegan butter and mix with a fork until clumps form. You want a sandy texture with some bigger crumbles.

Assemble: Spread the apple mixture evenly in the baking dish. Sprinkle the crumble topping over the apples, covering them completely without pressing down too hard.

Bake: Place the dish on the center rack and bake for 40–50 minutes, until the topping is golden brown and the apples are bubbling around the edges. If the top browns too quickly, tent loosely with foil for the last 10 minutes.

Rest: Let the crumble cool for at least 10–15 minutes so the juices thicken slightly. This makes it easier to scoop and keeps the filling saucy instead of runny.

Serve: Spoon into bowls and top with vegan vanilla ice cream or a dollop of coconut yogurt. Add a drizzle of maple syrup if you like it extra sweet.