Preheat your oven to 350°F (175°C).
In a large bowl, toss the sliced apples with a sprinkle of cinnamon and set aside.
In another bowl, combine oats, flour, brown sugar, and salt.
Pour in the melted butter and vanilla extract, mixing until crumbly.
Spread the apple mixture evenly in a greased baking dish.
Evenly sprinkle the oat mixture over the apples.
Bake in the preheated oven for 35-40 minutes, or until the top is golden brown.
Check the apples for tenderness; they should be soft.
Remove from the oven and let cool for a few minutes.
Serve warm, optionally with ice cream or whipped cream.