Preheat oven to 375 degrees F (190 degrees C). Spray an 8-inch square baking dish with cooking spray.
Stir water and flax seeds together in a bowl. Mix oats, pastry flour, sugar, raisins, chocolate chips, baking powder, and salt together in another bowl.
Beat peanut butter and maple syrup together in a bowl; add flax seed mixture and stir. Pour peanut butter mixture into oats mixture and stir until well-blended. Press mixture into prepared baking dish.
Bake in the preheated oven until set, about 15 minutes. Cool briefly before cutting into bars and transferring bars to a cooling rack.