For the barbecue sauce: In the bowl of a blender, combine the ketchup, apple cider vinegar, molasses, mustard, garlic, chipotles and sauce and onion. Season generously with salt and pepper. Blend until smooth.
For the ribs: In a small bowl, combine the garlic powder, paprika, brown sugar, cayenne, chili powder, 2 tablespoons salt and 2 teaspoons black pepper. Sprinkle the ribs with the rub on all sides.
In a skillet, warm the olive oil over medium-high heat. When shimmering, add the ribs and brown on all sides, working in batches if necessary. Transfer to a slow cooker.
Add the barbecue sauce, Mexican oregano and enough chicken stock to come halfway up the ribs. Set the slow cooker to high and cook, 8 to 10 hours. Remove the ribs and shred the meat into bite-sized pieces. (Discard the fat.) Taste the sauce and adjust the seasoning if necessary. Whisk to combine (the sauce may separate during cooking) and transfer to a serving bowl.
Construct tacos by spreading the tortillas with sauce and topping with pork, cucumbers, avocado wedges, cabbage, Cotija, radishes, pico de gallo and cilantro. Serve immediately with lime wedges.