Preheat your oven to 350°F, and lightly grease an 8x8 baking dish.
In a large bowl, mix together all the filling ingredients, then spread into the baking dish.
Mix the flour, brown sugar, and cinnamon in a medium bowl. Cut in the butter with a pastry cutter or fork until the mixture is crumbly. Stir in the oats, then sprinkle over the apples.
Bake for 35 to 40 minutes until the topping is golden and the filling is bubbly around the edges.
Remove from the oven and let it cool on a wire rack for 5 minutes before serving. Enjoy!