In a large bowl, combine the first 5 ingredients. Add chicken; mix lightly but thoroughly. Shape into 3/4-in. balls. In a large skillet, heat oil over medium heat. Brown meatballs in batches; drain. Transfer to a 4- or 5-qt. slow cooker., Add stock, tomatoes, onion, bok choy, carrots, red peppers, julienned serrano peppers, garlic and salt. Cook, covered, on low 6-8 hours or until meatballs are cooked through and vegetables are tender. If desired, stir in panko. Without stirring, drizzle beaten egg into slow cooker. Let stand until egg is set, 2-3 minutes. Freeze option: Before adding egg, cool soup. Freeze in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a saucepan, stirring occasionally; add broth if necessary. Without stirring, drizzle beaten egg into soup. Let stand until egg is set, 2-3 minutes.