Preheat oven to 350 degrees F. Prepare 2 large baking sheets by lining with parchment paper. Set aside.
In a large bowl, whisk egg, brown sugar and vanilla extract until combined. Next, add cocoa powder, baking powder, and salt, and whisk to combine.
Next, add sunflower seed butter. You will want to do this with a strong wooden spoon, stir very well until completely combined. Dough will be thick, stiff, and almost crumbly in texture.
Using your hands, roll dough into golf ball-sized balls and place on prepared baking sheets. The cookies do not spread much during baking so carefully press down on the dough balls to slightly flatten. Sprinkle each cookie with sunflower seeds.
Bake cookies for 8-10 minutes, until edges of cookies are set. Allow cookies to cool on the pan before transferring them to wire rack.