Preheat oven to 350°. In a large bowl, combine flour, brown sugar and salt. Cut in butter until crumbly. Pat into a greased 9-in. square baking pan. Bake until lightly browned, about 15 minutes. , Meanwhile, drain the peaches and reserve juice in a small saucepan. Stir in the sugar and cornstarch until smooth. Bring to a boil; cook and stir until thickened, 1-2 minutes. Remove from the heat; stir in peaches. , Pour over crust. For topping, combine oats, brown sugar and flour. Cut in the butter until crumbly. Sprinkle over filling. Bake until golden brown and bubbly, 25-30 minutes.