For the chicken, rinse chicken briefly, pat dry, cut into about 1 cm (approximately 1/2 inch) wide strips and stick on a skewer. Arrange skewers close together circularly on a plate. For the marinade, mix sweet soy sauce, soy sauce and sambal oelek together in a small bowl. Brush the marinade over chicken, cover and let rest for approximately 1 hour while turning chicken skewers over occasionally.
For the peanut sauce, peel shallots and garlic and finely chop. Puree peanuts in a blender or in a mortar. Add shallots, garlic, soy suace, sambal oelek, lemon juice and palm sugar to the blender and process into a paste. Heat oil in a small pan. Fry peanut paste fry for 2-3 minutes over medium heat. Deglaze the pan with coconut milk. Reduce the heat and simmer for 2-3 minutes while stirring. If the sauce is too thick, add a little water.
Preheat the oven broiler. Place chicken skewers on a grill pan or baking sheet and cook under the preheated oven broiler, watching carefully, for 5-6 minutes on each side. During the cooking time, brush chicken with remaining marinade. You can also cook chicken skewers in a pan with 3 tablespoons oil over medium heat for 5 minutes on each side. Arrange skewers on a plate and serve with the peanut sauce.