Preheat Oven: Preheat your oven to 375°F. Grease an 8x8-inch baking dish or pan lightly with butter or oil.
Prepare the Filling: Toss the apple slices in a bowl with sugar (or honey) and cinnamon. Spread the apples evenly in the prepared baking dish or pan.
Make the Crumble Topping: In a medium bowl, mix the oats, flour, and brown sugar. Add the melted butter and stir until the mixture resembles coarse crumbs.
Assemble the Crumble: Sprinkle the oat mixture evenly over the apples.
Bake: Bake for 30 minutes, or until the apples are tender and the topping is golden brown.
Cool and Serve: Let it cool for a few minutes, then serve warm. Optionally, top with yogurt, ice cream, or whipped cream.