Combine onion, garlic, chicken, chile powder, cumin, oregano, enchilada sauce, broth, vinegar, chipotle chiles, and cornmeal in a 4 or 6 quart slow cooker. (Mine was 6 quart, but I had plenty of extra room.)
Cook on low for 6-8 hours, or high for 4-5 hours. Shred chicken with 2 forks. Stir soup and add salt and pepper if desired.
Serve in bowls and top with cilantro, tortilla chips, and other toppings as desired.