1. Cut the chicken, plum, and celery into bite-sized pieces and cut the grapes in half.
2. Zest and juice the 1/2 lime, or use 3 whole limes if using key limes.
3. Roughly chop the cilantro.
4. In a bowl, mix the fruit, chicken, lime juice and zest together with all the remaining ingredients.
5. Chill for 1/2 hour and serve.