Creating Slow-Cooked Coconut Curry Chicken is simple when you follow these steps:

1. Prepare the Slow Cooker: Lightly grease the slow cooker with cooking spray or oil.
2. Add Chicken: Place the boneless, skinless chicken thighs in the slow cooker.
3. Mix the Sauce: In a separate bowl, whisk together coconut milk, chopped onion, minced garlic, grated ginger, red curry paste, soy sauce, fish sauce (if using), and brown sugar until well combined.
4. Pour Sauce Over Chicken: Pour the sauce mixture over the chicken thighs in the slow cooker, ensuring they are well coated.
5. Add Vegetables: Layer the sliced bell pepper on top of the chicken and sauce.
6. Season: Sprinkle with salt and pepper to taste.
7. Cook: Cover and cook on low for 6 to 8 hours or on high for 3 to 4 hours until the chicken is tender and cooked through.
8. Add Spinach: In the last 15 minutes of cooking, stir in the baby spinach until wilted.
9. Finish with Lime Juice: Once done, squeeze fresh lime juice over the dish for a bright finish.
10. Garnish: Serve hot, garnished with fresh cilantro.

Following these steps will guide you in creating a mouthwatering dish that is sure to impress.