Prepare slow cooker with cooking spray. Sprinkle chopped onions all over the bottom of the slow cooker.
In a small cup, combine salt, pepper, onion and garlic powder. Rub and press spice mixture all over pork.
Place pork inside your slow cooker on top of onions. Pour dark pop of your choice all over roast. Cook on low for about 8 hours.
Gently remove roast and set aside on a plate.
Dump remaining liquid from your slow cooker down the drain and wipe out slow cooker with paper towel as best you can. It doesn't have to be perfect.
Before returning roast back into slow cooker, remove any bone, fat or muscle sections from the roast. As you clean roast, throw pieces you will be eating back into slow cooker.
Next, using two forks, or your fingers, shred the meat.
Prepare homemade barbecue sauce if not using store bought. Add to your shredded meat and continue to cook on low until heated through; between 45 minutes to 1 hour. Use as much or as little sauce as you prefer.
Split buns and place in oven on broil to toast each half. Once halves start to brown, remove from oven, add cheese and put back under the broiler until cheese is melted and starting to brown. Using tongs, pinch piles of the pork mixture on top of each bun half and top with the other bun half. Serve and enjoy!