1Heat oven to 350ºF. In large bowl, mix all filling ingredients except pineapple and blueberries with spoon until well blended. Fold in pineapple and blueberries. Spread in ungreased 8-inch square pan.
2In small bowl, mix all topping ingredients except butter. Cut in butter, using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until particles resemble fine crumbs. Sprinkle over blueberry mixture.
3Bake 45 to 50 minutes or until golden brown and toothpick inserted in center comes out clean.
4Meanwhile, in 1-quart saucepan, mix brown sugar and cornstarch. Add enough water to reserved pineapple juice to measure 2/3 cup; stir into brown sugar mixture. Cook over medium heat, stirring constantly, until mixture boils. Boil and stir 1 minute; remove from heat. Stir in lemon juice. Serve over warm dessert.