Combine dates, water, and maple syrup in a small heavy saucepan over medium heat. Bring to a boil, then cook, stirring frequently, until most liquid is absorbed (about 12 minutes).

The mixture should look like a jam. Remove from heat and stir in zest. Cool completely.

Preheat oven to 400°F.

In a large bowl, whisk together flour, oats, baking soda, and salt. Beat sugar and butter with a mixer at medium speed until smooth.

Stir flour mixture into sugar mixture (it will be crumbly).

Coat an 11- x 7-inch baking pan with cooking spray.

Press 2 cups of mixture into the bottom of the pan. Spread date mixture over flour mixture. Sprinkle remaining flour mixture on top.

Bake for 20 minutes or until golden brown. Cool completely in pan on a wire rack, then cut into 20 bars.