In a microwave safe bowl, combine the onions, garlic, chili powder, chipotle chilis, oregano, and oil. Stir until all the ingredients are combined with the oil. Microwave on high for 5 minutes, stirring once at 2 ½ minutes. The onions will be translucent and there will be an aroma from the spices and chilis. Place mixture in the slow cooker.
Stir tomato sauce and sugar into the slow cooker.
In a medium bowl combine the milk and bread slices. Use a fork or your hands to mash it up into a paste. Add the turkey, season with salt and pepper, and then mix it until it combines with the milk paste.
Stir turkey into the slow cooker mixture and break up any large pieces. You want the turkey combined with the liquid. Cook for 4-6 hours on low. Mine cooked for the full 6 hours using a 6 quart slow cooker.
When it is done cooking, using a spatula or spoon, break the turkey filling up into as small pieces as possible. Stir in cilantro, scallions, and lime juice.