Place chicken breasts, thighs, and sliced onion into the insert of the slow cooker.
In a small bowl mix together balsamic vinegar, chicken broth, red wine, diced tomatoes, Italian seasoning, onion powder, granulated garlic, and red pepper flakes.
Pour sauce over the chicken, place top on, and set to cook 3 hours on high or 4-6 hours on low.
Place chicken in a medium to large bowl and drain the sauce into a medium sauce pan.
Keep chicken whole or shredded.
In a small bowl mix together cornstarch and water. Pour slurry into the pan with the sauce and cook over medium until the sauce becomes bubbly and thickens. As the sauce cooks stir in 1-2 tablespoons of honey, salt, and pepper. Taste for seasoning and then pour some of the sauce in with the chicken and save the rest to drizzle on top as needed.
Serve with vegetable, rice, in a wrap, or however you like.