Season all sides of ribs with salt, black pepper, garlic powder, onion powder & paprika very well.
Place a large deep skillet or Dutch oven over a medium high heat. Add in 3-4 TBS cooking oil. Heat oil until hot.
Once oil is sizzling add in ribs in one single layer. (It may need 2 batches, depending on how many ribs you have.)
Cook for 2-3 minutes on one side until golden brown and a crust forms from the seasoning. Turn over ribs and sear again for 3-4 minutes. Sear off other sides and ends of ribs. Remove from skillet onto a plate and finish last batch of ribs.
Spray the inside of a 6 quart crockpot with non-stick cooking spray. Layer 1/2 of the chopped onions inside of crockpot. Place half of the seared ribs on top of the onions. Layer the rest of onions on top of the ribs. Place remainder of the ribs on top of the onions.
Place 4-5 peeled & smashed garlic cloves on top of the ribs.
In a medium bowl whisk together barbecue sauce, mustard, garlic powder, onion powder, smoked paprika, salt, black pepper, and Worcestershire sauce. Taste for any seasoning adjustments.
Slather sauce all over the ribs. Cover crockpot and cook on high for 5-7 hours or on low for 8-10 hours. Remove ribs and make a thick gravy.Mix together corn starch and water and mix into juices in crockpot for a delicious gravy for your mashed potatoes and extra for the ribs. So GOOD.