Cover the chicken with thyme and sealed in cellophane, let it chill 12 hours. Take it out of the refrigerator 15 minutes before cooking.
Steam it for about 15 minutes (cooking time depends on the thickness of the chicken).
Remove the cellophane carefully so as not to burn, check for doneness (the chicken should not be pink) and let it cool well.
Then cut it into carpaccio and season with fresh thyme, oil, salt and pepper.