In a large bowl, mix together the oats, rice cereal, cocoa powder, coconut, and chopped nuts.
In a small bowl, stir together the coconut oil, maple syrup, and vanilla extract. Pour the liquid mixture over the dry ingredients and stir to cover evenly.
Transfer the mixture to a 9x13 inch baking dish (or similar). Bake for about an hour. It should bind together easily and feel solid to the touch.
Remove the granola from the oven and let it cool completely before breaking apart. Store in an airtight container.