Preheat oven to 180°C (350°F) and lightly grease a baking dish.
In a bowl, toss sliced peaches with sugar and a little flour or cornstarch to thicken the juices.
Spread the peach mixture evenly into the baking dish.
In another bowl, combine flour, oats, sugar, and butter; rub together until a crumbly texture forms.
Sprinkle the crumble mixture evenly over the peaches.
Bake for 30–35 minutes until the topping turns golden brown and the filling bubbles.
Let cool slightly before serving; enjoy warm with cream or ice cream if desired.