Spray the Crock Pot with cooking spray or put in a cooking liner. Layer the onion slices over the bottom of the pot and add a few tablespoons of the barbecue sauce.
Mix the spices and brown sugar together. Blend it with about 1/4th of the barbecue sauce, then coat all of the pork ribs. Place the ribs in the slow cooker, spacing them slightly apart. Add in about ½ cup of water, or enough to cover the bottom.
Cook the ribs on Low for 6 to 8 hours or on High for 3 to 4 hours. Test the meat after half of the time and remove the ribs when they reach 170 degrees F.
Warm up the remaining barbecue sauce and pour it over the ribs, then serve.
Notes
If you want more of a grill-style glaze on the ribs, consider placing the cooked ribs in a cast iron skillet. Brush them with the barbecue sauce and place them under your oven broiler for a few minutes.