Preheat your oven to 350°F (175°C). Lightly grease a 9-inch square baking dish or a similar 2-quart baking dish.
Prep the apples.
Peel, core, and slice them into even 1/4-inch slices. Thinner slices cook more evenly and soften nicely.
Make the filling. In a large bowl, toss the apples with coconut sugar, lemon juice, cinnamon, nutmeg, vanilla, cornstarch, and a pinch of salt.
Mix until the apples look glossy and evenly coated.
Transfer the apple mixture to the baking dish. Spread it out so the apples sit in an even layer.
Mix the topping. In a medium bowl, combine the oats, almond flour, coconut sugar, cinnamon, and salt.
Stir in the melted coconut oil or vegan butter until the mixture looks like slightly damp sand. If using nuts, fold them in.
Top the apples. Sprinkle the oat mixture evenly over the apples, covering most of the surface but leaving a few small gaps for steam to escape.
Bake for 35–45 minutes, until the topping is golden brown and the filling is bubbling around the edges.
If the top browns too quickly, tent loosely with foil for the last 10 minutes.
Cool for 10–15 minutes before serving. This helps the juices thicken, so your servings hold together.
Serve warm with dairy-free vanilla ice cream, coconut whipped cream, or a drizzle of warm oat milk.