Mix the oats and flaxseed in a bowl - make sure it's big enough to hold the oats and additional 1 cup of water.
In a microwave safe glass, heat the water until it starts bubbling - mine usually takes about two minutes.
Carefully remove the water from the microwave and pour over the oats, then place a large plate over the bowl and let it sit for at least 30 minutes.
Remove the plate and mix in the cocoa powder, adding a splash of water as needed to get a texture you like - you can also add a little sweetener at this stage, to your taste.