Begin by pre-heaing your oven to 325 ̊F. Next, mix the garlic powder, paprika, chili powder, ground fennel, cumin, salt, and pepper in a small bowl and set aside.
Now remove the membrane from the ribs (the silvery skin-like layer that covers the ribs). The easiest way to re- move the membrane is to slide a knife underneath it anywhere along the rack and slowly work it away. If it resists in one spot, find another spot to continue, lifting the membrane and loosening it with your knife until you can get a good grip on it. Eventually you will be able to peel the membrane off the ribs completely in a large sheet. If the membrane breaks, use your knife to restart at another section and repeat the process.
Once the membrane is removed, season both sides of each rack of ribs with the earlier-made spice rub and place them snugly side-by-side in either a large roasting pan or 13”x9” baking dish. Add the cubed onion and garlic cloves by stuffing them underneath, in-between, and on top of the racks of ribs, as well as 1 cup of water. Cover the pan with tin foil and bake for 3 hours.
During the last 15 minutes in the oven, start warming up your grill. Remove the ribs from oven and place them on the grill over medium heat, discarding the onions and garlic. Brush on the barbecue sauce and grill each side 5-7 minutes. Remove from grill and let rest for 10 minutes before serving.
