Fresh cilantro amped up with serrano, scallions, and lime make a lively sauce for juicy flame-kissed chicken.
Combine 1 tablespoon salt and 1/2 teaspoon pepper. Sprinkle mixture evenly on chicken, then set chicken on a rimmed baking sheet. Let stand uncovered 1 hour.
Meanwhile, chop cilantro; combine with serrano, scallions, lime zest and juice, and oil. Season with salt.
Heat a charcoal grill, creating a two-zone fire with vents partially open. Position coals on one side of the grill for direct high heat, and leave the other side empty for indirect lower heat. (On a gas grill, turn one side on high, and leave the other burners off.) Lightly coat chicken with olive oil and place over indirect heat. Cover and cook, turning occasionally, until pieces are cooked through and a thermometer inserted into thickest parts (not touching bones) registers 165 degrees, about 30 minutes.
Uncover grill; transfer chicken to direct heat. Brush dressing over chicken as pieces come off the grill.