Spray the inside of a 4 to 5 qt slow cooker with cooking spray.

Remove the inner skin from the pork back ribs.

In a small bowl, mix together the brown sugar, salt, pepper, and minced garlic.

Rub the brown sugar mixture into the ribs, ensuring they are evenly coated.

Cut the ribs into approximately 4-inch pieces for easier handling and cooking.

Layer the ribs and sliced onion in the prepared slow cooker.

Pour the cola over the ribs.

Cover the slow cooker and cook on a low heat setting for 8 to 9 hours, or until the ribs are very tender.

Remove the ribs from the slow cooker and drain and discard the liquid.

Pour barbecue sauce into a shallow bowl.

Dip each rib piece into the barbecue sauce to coat it thoroughly.

Place the coated ribs back into the slow cooker.

Pour any remaining barbecue sauce over the ribs to ensure they are fully covered.

Cover the slow cooker again and cook on a low heat setting for an additional hour to allow the sauce to meld with the ribs.