Combine dates and water in a small saucepan over low heat; cook and stir until dates are mostly dissolved, mashing larger pieces with a spoon, 10 to 15 minutes.
Mix oat flour, almond flour, and hemp seeds together in a large bowl.
Stir almond butter and vanilla extract into date mixture until well mixed. Mix date mixture into oat flour mixture using a pastry blender until well mixed. Press mixture into an 8-inch baking dish; refrigerate until chilled, about 30 minutes.