Marinate the chicken with the garlic, ginger, soya sauce, black pepper powder, brown sugar and vinegar. Thread the chicken onto earlier soaked skewers. Do not discard the marinade
Preheat a grill pan. Brush with some oil, once the pan is nice and hot, place the chicken yakitori on it, and cook by turning their sides, ensuring the chicken is well cooked. Mix the corn flour with water in a bowl to make slurry. Heat oil; add the garlic and sauté till it turns light brown.
Add the remaining marinade and the chili sauce and bring to a boil. Add the corn flour slurry and wait for the sauce to thicken. Once the sauce is thick, turn off the flame. Check the seasonings.
Transfer the sauce to a small bowl. To serve, transfer the chicken Skewers to a serving platter, pour the sauce over it or in a bowl and serve hot.