In a large bowl, combine the water, brown sugar, vanilla extract, and ground flax.
In a separate bowl, whisk together the pea protein, rice flour, cocoa powder, salt, cinnamon, xanthan gum, baking soda and baking powder.
Add the pea protein mixture (dry ingredients) to the wet ingredients. Mix together well.
Roll the dough into balls and flatten them out a bit. Place them on a parchment paper lined baking sheet. You should end up with 10 cookies.
Bake for 9 - 10 minutes.
While the cookies are baking, make the frosting. In a bowl, mix the avocado oil and powdered sugar together. I just use a fork until it reaches a frosting-like texture - think Oreo filling.
Once the cookies are baked, allow them to cool for at least 4 hours. Baked goods made with pea protein sometimes leak water within the first few hours after coming out of the oven, so it's important to allow them to fully cool and reach equilibrium before adding the frosting (because the frosting will melt if it touches water and you'll be feeling a lot like the sad little racoon who put his cotton candy in water).
Frost 5 of the cookies with the frosting, and place the remaining 5 cookies on top.