Step 1: Prepare the Chicken

1. Season the chicken thighs with salt and black pepper on both sides.
2. Optional: Heat a skillet over medium-high heat and sear the chicken for 2-3 minutes per side until golden brown. This step adds flavor but is not essential for slow cooking.

Step 2: Make the Hoisin Sauce

1. In a medium bowl, whisk together the hoisin sauce, soy sauce, honey, rice vinegar, sesame oil, garlic, ginger, and red pepper flakes (if using).

Step 3: Assemble the Slow Cooker

1. Place the chicken thighs in the slow cooker in an even layer.
2. Pour the prepared hoisin sauce over the chicken, ensuring each piece is well coated.
3. Add any optional vegetables around the chicken for a one-pot meal.

Step 4: Cook the Chicken

1. Cover and cook on low for 4-6 hours or on high for 2-3 hours, until the chicken is tender and fully cooked (internal temperature of 165°F/74°C).

Step 5: Thicken the Sauce (Optional)

1. If the sauce is too thin, remove the chicken from the slow cooker and transfer the sauce to a small saucepan.
2. Simmer the sauce over medium heat for 5-7 minutes, or until thickened to your liking.

Step 6: Serve and Garnish

1. Serve the chicken over steamed rice, noodles, or with a side of roasted vegetables.
2. Garnish with sliced green onions, sesame seeds, and fresh cilantro for a pop of flavor and color.