If you have a food processor, this is SO easy. To make this crisp, I peel, core, and slice about 4-5 apples, or enough to fill the baking dish I'm using. I throw the apples into the sprayed baking dish, then toss them around with a handful of flour, trying to evenly coat the apples.
In the food processor, I add oatmeal, brown sugar, and cinnamon. The amount of each ingredient can be adjusted depending on personal taste. I usually end up with about 1 cup oatmeal, a couple big spoonfuls of brown sugar, and a few heavy shakes of cinnamon. I then add a few tablespoons of cold butter, cut up into smaller pieces. Pulse in the food processor until the mixture becomes clumpy & it looks like a crumble topping. If it's not coming together, add more butter & pulse again. Spread the crumble on top of the apples, and you're done!
Bake at 350 for about 45 min- 1 hour. I know it's done when the topping is golden brown, and the apples at the bottom look like they're sort of bubbling. Enjoy!