01 - Layer the sliced red onion and minced garlic evenly across the bottom of the slow cooker insert to create a flavorful bed for the chicken.
02 - Place the chicken thighs in a single layer over the onion and garlic mixture, ensuring even cooking coverage.
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 each piece is coated with the glaze.
05 - Cover and cook on low setting for 6 hours or high setting for 4 hours, until the chicken reaches an internal temperature of 165°F and is tender throughout.
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 to 8 minutes until reduced and slightly thickened, then return the chicken to coat.
07 - Sprinkle freshly chopped parsley over the chicken before serving.