Preheat the oven to 350°F. Line a large baking sheet with parchment paper.
In a small bowl, combine the ground flax seeds and water. Let it sit to thicken while you prepare the rest of the ingredients.
In a large bowl, add the rolled oats, sugar, cocoa powder, baking soda, salt, sunflower seed butter, coconut oil, maple syrup, vanilla and chocolate. Add the flax egg and stir well to combine.
Scoop the dough to the prepared baking sheet, making 8 cookies. Form them into little mounds to limit the spreading. Don't flatten them too much or they will spread significantly.
Bake for 15 minutes at 350°F. Remove from the oven and let them cool for at least 10 minutes before eating. They will be delicate when warm.