Scrape the paper-thin skin off of the fresh ginger using the edge of a spoon and then grate the ginger with a cheese grater.
Combine the grated ginger, yogurt, salt and cumin in a bowl and whip to combine thoroughly.
Place the chicken halves in a Ziplock bag, add the marinade, seal the bag and refrigerate for at least 4 hours and up to 24 hours, turning the bag at least once.
Prepare your grill for indirect grilling by lighting one side on high and leaving the other side off. We are going to sear the chicken to get some great crispy skin and then roast with the lid closed on the cool side of the grill.
Remove the chicken from the marinade and place skin side down on the hot side of the grill. Watch for flare-ups at this point, that skin likes to drip its fat onto the coals and cause problems. If flare-ups occur, just slide the chicken over until the flames go out.
Continue to grill with the skin side down for a few minutes, until you get a nice brown skin.
Flip the chicken over and move it to the cool side of the grill.
Close the lid and maintain a temperature on the cool side of the grill of about 350 - 400 degrees. This is where a great probe thermometer comes in handy. Simply place the thermometer into the thickest part of the breast and roast the chicken until you hit 160 degrees.
Once the breasts hit 160 degrees, you are done! Remember to leave the lid closed as much as possible to maintain the heat.