Special equipment: Shot glasses
Put the watermelon, tomatillos, jalapeno, lime juice and zest, salt and pepper into a blender or food processor, working in batches if necessary. Blend until the mixture is smooth. Chill well before serving, at least 1 hour and up to 1 day. To serve, pour about 2 ounces of the gazpacho into shot glasses and garnish with a lime slice.