Peel cucumber if desired. Cut cucumber in half lengthwise, remove seeds with a spoon, quarter and dice into small, 1/4-inch cubes. Pick off cilantro leaves and reserve for garnish. Finely chop cilantro stems. Remove seeds and pith from Thai chilis and finely dice. In bowl, add diced cucumber, fresh lychees, cilantro stems, and diced Thai chilis. Stir to mix. Add lime juice and zest, honey, rice vinegar and salt. Toss gently with a spoon to combine. Garnish with fresh cilantro leaves. Serve.