01 - Layer the sliced red onion and minced garlic evenly across the bottom of the slow cooker insert.
02 - Place the chicken thighs in a single layer on top of the onion and garlic bed.
03 - Whisk together the balsamic vinegar, honey, chicken broth, Dijon mustard, olive oil, dried basil, dried oregano, salt, and black pepper in a small bowl until fully combined.
04 - Pour the balsamic mixture evenly over the chicken thighs, ensuring all pieces are coated.
05 - Cover and cook on low setting for 6 hours or on high for 4 hours, until the chicken is tender and reaches an internal temperature of 165°F.
06 - For a thicker sauce, remove the cooked chicken and set aside. Transfer the cooking liquid to a saucepan and simmer over medium heat for 5–8 minutes until reduced. Return the chicken to the sauce before serving.
07 - Sprinkle with chopped fresh parsley just before serving.