Mix the brine together in a large bowl by combining warm water, kosher salt, garlic, peppercorns and rosemary.
Submerge chicken in brine. Cover the bowl and refrigerate 30 minutes or up to 2 hours.
Drain chicken and pat dry with paper towels.
Prepare a grill fire to 350° with hickory or oak for smoke flavor.
Meanwhile, make the peanut sauce.
In a saucepan, combine peanut butter, soy sauce, Worcestershire sauce, brown sugar, Harissa, garlic, salt and pepper.
Whisk in 1/4 cup of water at a time until desired consistency is reached. Cook just until heated through. Set aside until ready to use.
Place chicken over indirect heat and cook with the grill closed about 15 minutes.
Brush chicken with peanut sauce in a thick coat.
Continue to cook chicken until internal temperature reaches 165° with a digital thermometer, about 10 minutes.
Remove from grill and allow to rest 10 minutes before serving.