Preheat oven to 375 degrees Fahrenheit. Grease a 9"x9" metal baking pan. Line pan with foil; grease foil.
Prepare Oat Crust & Topping: In a large bowl, with hand, mix flour, oats, brown sugar, butter, baking soda, salt, and cinnamon until mixture comes together. Transfer 2 cups mixture to baking pan; reserve remaining mixture for crumb topping. With hand, press mixture evenly onto bottom of pan to form a crust. Bake crust 10 minutes. Cool completely in pan on wire rack. Turn off oven.
While crust is cooling, prepare Date Filling: In 2-quart saucepan, cook dates, brown sugar, and water over medium heat until mixture thickens and all liquid is absorbed, about 6 to 8 minutes, stirring frequently. Spoon Date filling into bowl; refrigerate until cool, about 30 minutes.
When filling is cool, preheat oven to 375 degrees Fahrenheit. Spread filling over crust; top with reserved crumb mixture. Bake 35 to 40 minutes, until topping is golden. Cool completely in pan on wire rack.
When cool, transfer with foil to cutting board. Cut into 4 strips, then cut each strip crosswise into 3 pieces.