In a large bowl, combine the soy sauce, ketjap manis, vegetable oil, lime juice, minced garlic, grated ginger, ground coriander, ground cumin, ground turmeric, and ground black pepper.
Add the chicken pieces to the marinade and toss to coat evenly.
Cover and marinate in the refrigerator for at least 30 minutes, preferably longer for more flavor.
In a saucepan, combine the peanut butter, coconut milk, soy sauce, ketjap manis, lime juice, brown sugar, minced garlic, ground cumin, ground coriander, and ground chili powder (if using).
Cook over medium heat, stirring constantly, until the sauce is smooth and well combined.
Add water as needed to achieve the desired consistency. The sauce should be thick but pourable.
Remove from heat and set aside.
Thread the marinated chicken pieces onto the soaked wooden skewers.
Preheat a grill or grill pan over medium-high heat.
Grill the chicken skewers for about 4-5 minutes on each side, or until the chicken is cooked through and has nice grill marks.
Enjoy your meal!