Let's make the sauce first. In a small mixing bowl, add your tomato paste, Worcestershire sauce, vinegar, garlic powder, sugar and water. Mix well.
In your slow cooker, add your pork tenderloin, white onion, sage and salt.
Add in your barbecue sauce. With a pair of tongs, mix the pork well into the sauce, flipping it around until all sides have sauce on them.
Cook for 6 hours on low.
After 6 hours, add in your apple and brussel sprouts. Cook for 2 more hours on low.
Recommended to serve over some wild rice!