Preheat the oven to 350°F (175°C).

Peel, core, and dice the apples into uniform pieces.

In a large bowl, combine the diced apples, granulated sugar, lemon juice, and ground cinnamon, tossing to coat.

Pour the apple mixture into a 9x13 inch baking dish and spread it evenly.

In a separate bowl, mix the rolled oats, all-purpose flour, packed brown sugar, and cold unsalted butter; use your fingers to crumble until the mixture resembles coarse crumbs.

Evenly sprinkle the crisp topping over the apples in the baking dish.

Bake for 35 minutes, or until the topping is golden brown and the apple filling is bubbly.

Let the apple crisp cool for at least 10 minutes before serving.