Rub salt and pepper over roast. Transfer to a 5- or 6-qt. slow cooker. In a small bowl, mix the mango nectar, pineapple, chutney, lemon juice and zest. Add to slow cooker. Cook, covered, on low until meat is tender, 6-8 hours. Cool slightly.
Remove roast from slow cooker. When cool enough to handle, shred meat with two forks. Strain cooking juices, discarding fruit; skim fat. Return cooking juices and meat to slow cooker. Stir in green onion. Serve on buns. If desired, top with jalapeno.