Store the can of coconut cream in the fridge overnight. I usually just keep one in the fridge.
Use a spatula to add all the coconut cream to the bowl of your stand mixer or the bowl you use your hand mixer with. I like to use one that has a lid with a small opening at the top so that the splatter is somewhat controlled.
Whip the coconut cream with your stand- or hand mixer for about a minute until it's smooth and creamy. I have never gotten it to gain much volume but that's fine.
Chop and melt the chocolate over a double boiler or in the microwave, whatever you prefer. Get it very warm and runny, don't temper it.
Pour all the chocolate into the bowl with the coconut cream and mix again with your stand-/hand mixer. Make sure to mix thoroughly.
Note: make sure that the chocolate is hot when you pour it in. If it's too cool, it'll harden too quickly and instead of a homogeneous mousse you'll get coconut cream with small chards of chocolate. Nothing wrong with that and if it's what you prefer, go for it. It resembles stracciatella gelato which is also very tasty.
Transfer mixture into a storage container, cover and cool in the fridge for at least 3 hours.