In a saucepan over medium-high heat, melt the butter. Add the garlic and stir for a few seconds. Add rice and saute for 1 minute, stirring constantly. Slowly pour in chicken stock, 3/8 tsp salt, and bring to a boil. Cover and reduce heat to low. Simmer for 15 minutes, or until all the liquid is absorbed, and rice is tender. Remove from heat, and let stand for 5 minutes. Add parsley and black pepper, fluff with a fork.
Preheat broiler to high. Line a jelly roll pan with foil, and spray with nonstick spray.
In a small bowl combine brown sugar, chili powder, paprika, cumin, garlic powder, and cayenne. Sprinkle 1/2 of the mixture over the chicken. Place chicken on prepared baking sheet. Broil for 5 minutes. Turn and sprinkle the remaining spices over the chicken. Broil for an additional 5 minutes, or until the chicken is cooked through.
Remove chicken from the pan, and let stand for a couple minutes. Scoop any pan drippings over the chicken to serve.