Preheat your oven to 350°F (175°C).
Line a baking sheet with parchment paper.
In a large mixing bowl, whisk together the whole-wheat pastry flour, cocoa powder, corn starch, salt, and baking powder.
In another bowl, combine the mashed avocado, softened butter, and Splenda. Beat them together until smooth and creamy. Then, add the vanilla, egg, and egg yolk, mixing until fully incorporated.
Gradually add the dry mixture to the wet mixture, stirring until just combined.
Gently fold in the chocolate chips and chopped peanuts using a spatula.
Using a cookie scoop or a tablespoon, drop rounded balls of dough onto the prepared baking sheet.
Bake for 10-12 minutes until set but soft in the center.
Let the cookies cool on the baking sheet for 5 minutes before transferring them to a cooling rack.