01 - Layer the thinly sliced onions and minced garlic evenly across the bottom of the slow cooker.
02 - Place the chicken breasts on top of the onion and garlic bed in a single layer.
03 - In a mixing bowl, whisk together the balsamic vinegar, chicken broth, honey, olive oil, Dijon mustard, dried basil, dried oregano, salt, and black pepper until fully incorporated.
04 - Pour the balsamic mixture evenly over the chicken breasts. Cover the slow cooker and cook on high for 4 hours or on low for 6 to 8 hours, until the chicken is tender and reaches an internal temperature of 165°F.
05 - Transfer the chicken and onions to a serving platter. For a thicker sauce, pour the remaining liquid into a saucepan and simmer over medium heat for 3 to 5 minutes until reduced to desired consistency.
06 - Spoon the onions and sauce over the chicken. Garnish with chopped fresh parsley if desired and serve immediately.