Preheat the oven to 350°F (175°C). In a mixing bowl, combine sliced peaches, sugar, lemon juice, and cornstarch. Toss to coat the peaches evenly.

In another bowl, mix together rolled oats, flour, brown sugar, melted butter, and cinnamon until crumbly.

Spread the peach mixture into a baking dish and evenly sprinkle the oat topping over the peaches. Bake for 30 minutes or until the topping is golden brown and the peaches are bubbly.

Let cool slightly before serving. Enjoy warm, optionally with vanilla ice cream.