Preheat the oven to 375 degrees. To make the crumb topping, simply combine the oats, brown sugar, flour, melted butter, and a pinch of salt. Stir to form a crumbly topping. To make the filling, toss the sliced peaches with sugar, salt, and cornstarch in a 9×13 baking dish. Sprinkle evenly with the crumb mixture. Bake for 35-40 minutes, until topping is golden brown and peach filling is bubbly.