Combine the chicken with the rest of the ingredients in a covered casserole dish or plastic bag and marinate in the refrigerator for 1 hour or overnight.
Make the relish by combining the ingredients in a large bowl. Refrigerate until ready to serve to let the flavors meld.
When you’re ready to eat, preheat grill to medium-high heat. Remove the relish from the refrigerator so it can come to room temperature while you’re grilling the chicken.
Grill the chicken until done. Allow to rest for about 5 minutes. Top with the relish.