Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking dish or a similar-sized dish.

1. In a large bowl, combine the sliced strawberries, granulated sugar, lemon juice, and cornstarch (if using). Stir to combine, and then pour the strawberry mixture into the prepared baking dish, spreading it evenly.
2. In a separate bowl, mix together the oats, flour, brown sugar, cinnamon, and salt. Add the cold, cubed butter to the mixture, and use your fingers or a pastry cutter to work the butter into the dry ingredients until the mixture resembles coarse crumbs.
3. Sprinkle the crumble topping evenly over the strawberries.
4. Bake the crisp in the preheated oven for 35-40 minutes, or until the topping is golden brown and the filling is bubbling.
5. Remove from the oven and let it cool slightly before serving.
6. Serve warm, optionally with a scoop of vanilla ice cream or a dollop of whipped cream.