Season the ribs all over with salt and pepper, then brush with the vegetable oil. Combine the brown sugar, chile powder, cumin and oregano in a small bowl. Sprinkle the spice mixture all over the ribs and rub into the meat. Transfer the ribs to a 6- to 8-quart slow cooker. Cover and cook on low, 7 1/2 hours.
Preheat the broiler and line a baking sheet with foil. Whisk the barbecue sauce with the agave in a bowl. Transfer the ribs to the prepared baking sheet and brush both sides with half of the barbecue sauce mixture. Turn bone-side down and broil until the glaze is bubbling and browned, 3 to 5 minutes.
Slice the ribs between the bones and top with cilantro. Serve with lime wedges, cornbread and the remaining barbecue sauce.