1. Whisk marinade ingredients together. Trim excess fat from the chicken.
2. Smear marinade all over chicken, inside and outside. Place skin side down in a pan, cover, and refrigerate overnight.
3. Drizzle olive oil on the bottom of a six to eight-quart Crock-Pot. Slice onion thickly into half-circles and place in pot. Carefully place chicken, skin side down, on onions.
4. Scrub sweet potatoes and cut in half lengthwise. Place on and around the chicken.
5. Pour marinade over all. Turn on high and cook for five hours, or until ready.