1 part Cayenne Pepper
2 parts Paprika
2 parts Chili Powder
2 parts Dijon mustard
Olive Oil

For "part" you have to decide based on how much chicken you are cooking.
1 part = 1 tablespoon works, but you may want to double that recipe to make sure you don't run out.
Place all the dry ingredients in a bowl, add the mustard, and then add just enough olive oil to make a nice paste that you can brush onto the chicken.
Whisk it all together and apply to both sides of the boneless chicken breasts.

The chicken will cook in about 20 minutes, so you want to time putting it on the grill with when you want to eat, keeping in mind other meats like ribs are the slow end of the bargain.
Also, make sure that the grill is hot when you first put the chicken on to sear the outside.
Generally, it is a good idea to move the ribs up to the warming grid while doing this, and then when the chicken is seared on both sides on High heat, turn down to medium and get the ribs back down on the grilling surface.

Don't be afraid of the spice on these--the fire cooks all the heat out and leaves behind a fairly mellow flavor that even spice-averse kids handle with ease.
To make it even more savory, serve with a little dish of apricot chutney.