Light your grill to about medium heat (if your chicken breasts are real thin, high heat will do).
Place all of the spices in a coffee grinder and grind until everything is the same size.
Rinse and pat the chicken breasts dry and then rub them all over with the spice rub.
Once the grill is ready, place the chicken breasts on the grill over the hottest section. We want a little sear, then move them over medium heat to finish if your breasts are a little on the thicker side.
Continue to grill the chicken for about 8 minutes per side over medium heat, or around 5 minutes per side over high heat (thinner breasts). Note, these are guidelines for times, it all depends on your grill and the thickness of your chicken breasts. Don't overcook the chicken, but make sure it cooks all the way through. One way to tell is by feel. Push on the tops of the chicken breasts. We want them to be firm, the indention from your finger should "spring back" relatively quickly. If you can still see the indention after a few seconds, they probably aren't done in the middle. Takes a little practice, but the grilling by feel technique will prevent you from having to pierce the meat.
Remove from the grill, allow the chicken breasts to rest for about 5 minutes and then serve!