Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the sliced peaches, granulated sugar, lemon juice, and ground cinnamon. Toss until the peaches are evenly coated.
Pour the peach mixture into a greased 9x13 inch baking dish.
In another bowl, mix together the rolled oats, all-purpose flour, brown sugar, and salt.
Pour in the melted butter and stir until the mixture is crumbly and well combined.
Sprinkle the oat topping evenly over the peach mixture.
Bake in the preheated oven for 30-35 minutes, or until the topping is golden brown and the peaches are bubbly.
Let cool for about 10 minutes before serving.