Sprinkle pork with salt and pepper. In Dutch oven, heat oil over medium-high heat; brown pork all over. Transfer to slow cooker. Add onions, garlic, chili powder, coriander and bay leaves to Dutch oven; cook, stirring often, until onions are softened, about 5 minutes. Add tomato paste; cook, stirring, until darkened, about 2 minutes. Add tomato sauce, sugar, vinegar and Worcestershire sauce, scraping up any browned bits. Pour into slow cooker. Cover and cook on low until pork is tender, 8 to 10 hours. Transfer pork to cutting board and tent with foil; let stand for 10 minutes. With 2 forks, shred or “pull” pork. Meanwhile, pour liquid from slow cooker into large saucepan; skim off fat. Bring to boil over high heat; boil vigorously until reduced to 3 cups, 10 to 12 minutes. Discard bay leaves. Add pork; stir to coat and warm through. Sprinkle with green onions.