Preheat your oven to 350°F (175°C). This ensures that the crisp cooks evenly and the topping becomes golden brown.

In a large mixing bowl, combine the sliced peaches, granulated sugar, lemon juice, cornstarch, and ground cinnamon. Stir gently until the peaches are evenly coated. The sugar will help draw out the juices from the peaches, creating a delicious filling.

Transfer the peach mixture into a 9-inch baking dish, spreading it out evenly.

In another mixing bowl, combine the rolled oats, all-purpose flour, brown sugar, and salt. Mix well to ensure the dry ingredients are evenly distributed.

Pour the melted butter into the dry mixture. Use a pastry cutter or fork to combine until the mixture resembles coarse crumbs. This will create a crunchy topping when baked.

Sprinkle the oat mixture evenly over the peach filling in the baking dish.

Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the topping is golden brown and the peach filling is bubbly. The baking time may vary depending on your oven, so keep an eye on it.

Once baked, remove from the oven and let it cool for about 10 minutes before serving. This allows the filling to set slightly, making it easier to serve.