Combine the soy sauce, lemon juice, scallions, garlic, and 1/4 teaspoon pepper in a resealable plastic bag. Add the chicken pieces; seal and toss well to coat. Place in the refrigerator and marinate overnight.
Prepare a grill for indirect-heat cooking or preheat a grill pan over medium heat. Preheat an oven to 450 degrees F. Combine the brown sugar, ginger, water, and hoisin sauce in a glass bowl as a basting sauce.
Remove the chicken from the marinade and pat dry. Place on the grill, skin-side down and cook until the skin is well marked, 6 to 8 minutes, keeping a close eye. Turn the chicken and basting constantly, cook the chicken for another 5 minutes. Transfer the chicken, skin-side up, to a baking sheet.
Generously brush the chicken with the sauce and cook in the hot oven until the skin is crispy and the chicken is cooked through, about 15 to 20 minutes.
Let rest under a foil tent for 10 minutes, then it's "nom-nom" time.
Cook's Note: The key to tender chicken meat and caramelized crispy skin is basting the chicken first with the hoisin-ginger sauce and finishing the chicken in a high-heat oven.