Pour the olive oil on the bottom of the slow cooker, arrange the sliced onions over the oil, then put in all the dried herbs and garlic cloves. Pour in vinegar and top with tomatoes. Add salt and pepper to taste. Mix well.
Place chicken breasts down into the mixture and cover well. Cook on low for 6 hours.
Serve over rice or pasta.
Feel free to substitute pasta or your favorite whole grain for the brown rice. Nutritional information was calculated using brown rice.