Preheat the oven to 350 degrees. Spray a 8x8-inch baking dish with nonstick cooking spray.
Place the flax or chia seeds in a food processor, spice grinder, or coffee grinder. Grind the seeds into powder and place it in a small bowl. Add the water and stir. Allow the mixture to sit and thicken for 15 minutes to create “flax eggs” or “vegan egg substitute.”
Meanwhile, pour 2 1/2 cups of oats into the food processor and grind into fine oat flour.
Place the brown sugar and vegan butter into the bowl of an electric mixer. Beat on high to cream the “butter” and sugar together until light and fluffy, 3-5 minutes.
Roughly chop the nuts. Then remove the pits from the dates and chop into small pieces.
Scrape the mixing bowl with a spatula and add the vanilla, cinnamon, salt, oat flour and remaining oats. Beat on low. Add in the flag "eggs” and continue to beat until smooth.
Finally, turn the mixer on low and mix in the dates and nuts. Scoop the mixture into the prepared baking dish. Spread the batter out evenly, then sprinkle the top with extra oats if desired.
Bake for 45 minutes, or until the center is puffed and doesn’t jiggle when you shake the pan. Cool the bars completely. Then cut into 16 squares. Store in an airtight container for up to one week.
If using some sort of vegan powdered egg substitute, add enough powder and water to create 2 eggs.