Preheat oven to 400 °F. Grease a 9 x 13 inch baking pan. In a small saucepan, combine white sugar and cornstarch. Add pineapple and juice. Cook over medium heat until thick, set aside.
In a mixing bowl, combine flour, brown sugar, baking soda, salt and oats; cut in butter until mixture is crumbly. Pat half of dough firmly into prepared pan.
Pour pineapple mixture over dough; pat remaining dough firmly over pineapple mixture. Bake for 25 - 30 minutes. Cool in pan; cut into bars.