Cut watermelon into small chunks, removing both the outer rind and the seeds.
Freeze the watermelon chunks for at least 4-5 hours.
Add the watermelon chunks to a food processor with half of the coconut milk. Process the mixture until smooth, adding in the rest of the coconut milk, as needed, to help the process go more smoothly, and to make a creamier watermelon ice cream.
Scoop the watermelon ice cream into bowls for serving immediately. If you want to make a more solid ice cream, store in the freezer for more time, as needed.