Roughly chop the chili peppers. If they are dry you can just break them with your hands.
Place them in a small saucepan and add the water. Place the pan over medium heat and bring to boil. Lower the heat and let simmer for 2-3 minutes. Remove the pan from the heat and let cool until room temperature.
Pour 150 ml of the water through tea stainer or a fine sieve into a measuring cup. You would need only this quantity for the mousse.
Melt the chocolate in a bowl over a pan of simmering water. Transfer it into a large mixing bowl and add the 150 ml spicy water. Place the bowl in a pan full of ice and start whisking energetically with a hand whisk. Continue for 5 to 10 minutes or until the chocolate mousse starts getting thick. Be careful not to overheat as the structure of the mousse will become grainy (if this happens, melt it again and repeat the whisking).
Pour the chocolate mousse into small ramequins or glasses. Cover them with cling film and refrigerate. Before serving pipe or spoon the garnish on top.