01 - Layer the sliced red onion and minced garlic evenly across the bottom of the slow cooker insert.
02 - Place the boneless, skinless chicken thighs in a single layer on top of the onion and garlic bed.
03 - In a small mixing bowl, whisk together balsamic vinegar, honey, chicken broth, Dijon mustard, olive oil, dried basil, dried oregano, salt, and black pepper until fully incorporated.
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 high setting for 4 hours, until chicken reaches 165°F internally and is tender throughout.
06 - For a thicker sauce, transfer the cooked chicken to a platter. Pour the cooking liquid into a saucepan and simmer over medium heat for 5-8 minutes until reduced. Return the chicken to the sauce before serving.
07 - Sprinkle with fresh chopped parsley just before plating. Serve over rice, mashed potatoes, or with steamed vegetables.