1. In a medium bowl, whisk together the soy sauce, honey, ketchup, vinegar, minced garlic, black pepper, and red pepper flakes (if using). Ensure everything is well combined to form a smooth, flavorful sauce.

2. Place the chicken thighs or breasts into the bottom of your crockpot in a single layer. No need to sear or brown them beforehand — the slow cooking will make them tender and juicy.

3. Pour the sauce mixture evenly over the chicken in the crockpot, ensuring all pieces are well coated. Cover with the lid and cook on low for 4-5 hours or on high for 2-3 hours, depending on your schedule and desired tenderness.

4. About 20 minutes before serving, mix the cornstarch and water together in a small bowl to create a slurry. Pour it into the crockpot and gently stir. Cover again and let it cook for another 15-20 minutes. The sauce will thicken into a glossy glaze.

5. Once the sauce has thickened and the chicken is fully cooked, garnish with chopped parsley or green onions. Serve hot over your favorite side like white rice, brown rice, noodles, or vegetables.