Step 1: Heat vegetable oil in a large skillet or Dutch oven over medium-high heat. Season chicken pieces with salt and black pepper, then add to the skillet. Cook for 5-6 minutes until browned on all sides. Remove chicken and set aside.
Step 2: In the same skillet, add onion and cook for 3-4 minutes until softened. Add garlic, ginger, and red bell pepper, cooking for another 2 minutes until fragrant.
Step 3: Pour in coconut milk, soy sauce, brown sugar, turmeric, and red pepper flakes (if using). Stir well to combine.
Step 4: Return the browned chicken to the skillet, stirring to coat in the sauce. Reduce heat to medium-low, cover, and simmer for 15-20 minutes until chicken is cooked through and sauce has thickened slightly.
Step 5: Taste and adjust seasoning with salt and pepper if needed. Garnish with fresh cilantro and serve hot over cooked rice.