In a bowl, mix together ground coriander, ground cumin, turmeric powder, brown sugar, soy sauce, minced garlic, minced ginger, lemongrass, coconut milk, vegetable oil, and salt.
Add the chicken pieces to the marinade, ensuring they are well-coated. Cover and refrigerate for at least 1 hour, preferably overnight for deeper flavor.
In a saucepan, combine the ground peanuts, coconut milk, soy sauce, brown sugar, tamarind paste, minced garlic, and red chilies if using.
Cook over medium heat, stirring frequently until the mixture thickens. If the sauce is too thick, add water a little at a time until you reach the desired consistency.
Season with salt to taste. Remove from heat and let it cool.
Thread the marinated chicken pieces onto the soaked bamboo skewers.
Preheat a grill or grill pan over medium-high heat. Lightly oil the grill grates.
Grill the skewers for 3-4 minutes on each side, or until the chicken is cooked through and has a nice charred exterior.
Enjoy your meal!