Begin by preparing the chicken. Trim any excess fat from the chicken thighs and cut them into bite-sized pieces.
In a mixing bowl, combine the coconut milk, yellow curry powder, and fish sauce (if using). Whisk to combine.
Place the diced onions, minced garlic, minced ginger, potatoes, carrots, and red bell pepper in the slow cooker.
Add the chicken pieces on top of the vegetables, ensuring they are evenly distributed.
Pour the coconut milk mixture and chicken broth over the chicken and vegetables. Stir gently to combine, making sure the chicken is coated with the sauce.
Season with salt and pepper to taste.
Cover the slow cooker and set it to cook on low for 6-8 hours until the chicken is tender and the flavors meld together.
Once cooking is complete, taste and adjust seasoning if necessary. Serve hot, garnished with fresh cilantro if desired.