1Heat oven to 350°. Grease bottom and sides of jelly roll pan, 15 1/2x10 1/2x1 inch, with shortening, or spray with cooking spray. Beat flour, oats, brown sugar, butter, salt and baking soda in large bowl with electric mixer on medium speed until crumbly, or mix with spoon. Press about 4 cups of the mixture in pan.
2Beat remaining ingredients except rhubarb in large bowl with electric mixer on medium speed until blended. Stir in rhubarb. Spread over crust. Sprinkle with remaining crumb mixture; press lightly.
3Bake 40 to 50 minutes or until center is set; cool 30 minutes. Cover and refrigerate at least 3 hours but no longer than 48 hours. For bars, cut into 10 rows by 6 rows. Store covered in refrigerator.