Authentic Wonton Soup

Rub pork tenderloin with 2 tablespoons hoisin sauce. Season with red pepper flakes. Place pork tenderloin in a slow cooker. Cook on High until tender, 3 to 4 hours. Cool until easily handled, about 10 minutes. Chop into small pieces. Mix remaining 2 tablespoons hoisin sauce, ground pork, shrimp, bread crumbs, rice vinegar, cilantro, ginger, and soy sauce together in a large bowl. Place a 3/4-inch round ball of ground pork filling in the center of each wonton wrapper. Brush edges with water; fold and seal. Bring chicken stock and beef stock to a low boil in a large pot. Stir in pork tenderloin. Add wontons; cook until ground pork filling is no longer pink in the center, about 7 minutes. Reduce heat to very low. Serve soup garnished with green onions.