1. Preheat oven to 325°.
2. To prepare crust, weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 5 ingredients (through cinnamon) in a medium bowl, stirring well with a whisk. Drizzle butter and juice over flour mixture, stirring until moistened (mixture will be crumbly). Reserve 1/2 cup oat mixture. Press remaining oat mixture into the bottom of an 11 x 7–inch baking dish coated with cooking spray.
3. To prepare filling, combine dates, sour cream, and remaining ingredients in a medium bowl, stirring well. Spread date mixture over prepared crust; sprinkle reserved oat mixture evenly over filling. Bake at 325° for 40 minutes or until edges are golden. Cool completely in pan on a wire rack.