Combine soy sauce, banana ketchup, pepper, Sprite, lemon juice, garlic, ginger, sugar, and salt in a bowl; add chicken and toss to combine. Cover and refrigerate overnight.
Light a grill. Thread chicken onto skewers, reserving marinade, and brush with oil; grill, turning as needed and brushing with reserved marinade until charred and cooked, about 12 minutes. Transfer to a serving platter and garnish with scallions and crispy garlic.
