Preparation of Ribs: In a small mixing bowl, combine the salt, oregano, garlic powder, black pepper, chili powder, and paprika. Ensure that the membrane on the back of the ribs has been removed for better seasoning penetration. Apply the spice mixture generously to the meaty sides of the ribs, ensuring even coverage through gentle rubbing.
Setting the Slow Cooker: Place the sliced onions at the bottom of the slow cooker and pour the root beer over them. Position the seasoned ribs on top of the onions, cutting the ribs as necessary to fit within the cooker. Secure the lid and set the cooker to high for 3-4 hours or low for 6-7 hours, depending on your schedule.
Sauce Preparation: While the ribs are cooking, prepare the BBQ sauce. Heat olive oil in a medium saucepan over medium heat. Add chopped onions and minced garlic, sautéing until onions are translucent and soft, approximately 7-8 minutes. Pour in root beer and bring to a boil, allowing it to reduce by half over 5-7 minutes. Integrate the BBQ sauce, apple cider vinegar, brown sugar, minced chipotle, and Worcestershire sauce into the pan. Season with salt and black pepper, adjusting quantities to taste. Simmer the mixture for an additional 10-15 minutes to thicken.
Blending the Sauce: Once the sauce has slightly cooled, transfer it to a blender or use an immersion blender to puree until smooth. If not using immediately, the sauce may be stored in the refrigerator.
Broiling the Ribs: Upon completion of the cooking time in the slow cooker, preheat your oven's broiler and position a rack approximately 4-6 inches from the heat source. Line a large baking sheet with aluminum foil. Carefully transfer the ribs from the slow cooker to the baking sheet, handling them gently as they will be very tender. Generously brush the ribs with the prepared BBQ sauce. Broil for 2-3 minutes or until the sauce begins to bubble and caramelize. Monitor closely to prevent burning.
Serving: Serve the ribs hot, accompanied by additional BBQ sauce on the side for added flavor.