Preheat oven to 350° and grease an individual bar pan or a 9x11 inch baking pan
Combine the flax seed and water in a small bowl and let thicken for ten minutes
Whisk the flour, cinnamon, baking powder, and salt together in a large bowl. Add the maple syrup, peanut butter, whole oats, flax egg, walnuts, and water together and blend until combined. Stir the chocolate chips evenly throughout the batter.
Spoon into a bar pan or spread flat in a 9x11 inch baking pan and bake for 30 minutes or until golden brown.
Store in an airtight container in the refrigerator for up to one week, or freeze for up to three months.