Cut the chicken thighs into bite-sized pieces and place them in the slow cooker.
In a medium bowl, whisk together the soy sauce, brown sugar, garlic, ginger, and chili flakes until well combined. Pour the sauce over the chicken and stir gently so all the pieces are coated.
Cover and cook on low for 4–5 hours or high for 2–3 hours, until the chicken is tender and fully cooked.
In a small bowl, whisk the cornstarch with a little water to create a slurry. Stir it into the slow cooker during the last 30 minutes of cooking to thicken the sauce.
Once the sauce has thickened, stir the chicken to coat evenly before serving.
Slow Cooker Tips
Chicken thighs work best for this recipe because they stay tender during long cooking times. Chicken breasts can be used, but they may cook slightly faster.
If you want extra texture, you can quickly broil the cooked chicken on a baking sheet for a few minutes before serving. This helps caramelize the sauce slightly.
For added vegetables, stir in broccoli florets, bell peppers, or snap peas during the last 30 minutes of cooking.
Taste the sauce before serving and adjust sweetness or heat if needed by adding a little honey or extra chili flakes.