Lay the chicken breasts in a slow cooker, and set to low.
In the bowl of a food processor fitted with a chopping blade, place the onions, garlic, ketchup and apple cider, and pulse about 10 times to break up the onion and garlic.
Add mustard, molases, apple cider vinegar, Worcestershire sauce, and chili powder. Pulse about 5 more times until ingredients are combined.
Add tomatoes and pulse 2-3 more times to combine, leaving some tomato chunks.
Add salt and pepper, and adjust to taste.
Pour sauce over the chicken. Cover and cook on low for about 3 hours.
Turn slow cooker heat up to high.
Shred chicken with 2 forks, and add corn and sweet potato. Stir to combine.
Pour cornbread batter evenly over all.
Cover, and cook on high for another 1 1/2 to 2 hours, or until a toothpick inserted into the center of the cornbread comes out clean.