Make spice mix: combine cumin seeds, peppercorns and coriander seeds in a skillet over medium heat. Toast until fragrant, a few minutes. Finely grind toasted spices. Transfer to a small bowl and add sugar and salt.
Make lime mojo: combine all ingredients.
Rub spice mix on chicken and place in a ziploc bag with lime mojo. Refrigerate at least 1 hour.
Barbecue (or bake) chicken until cooked through. Serve.