Place Brussel sprouts on one side of the crockpot. Next, place carrots, potatoes and red onion in the crockpot.
Place the chicken breast on top of the vegetables.
In a medium sized bowl mix together balsamic vinegar, chicken broth, honey, ground mustard, rosemary, oregano, red pepper flakes, and garlic.
Pour the balsamic marinade on top of the chicken and vegetables and cook on low for 6 hours.