In a large bowl, combine ground chicken, panko breadcrumbs, egg, soy sauce, grated ginger, minced garlic, and sliced green onions. Mix gently until just combined without overworking the meat.
Form the mixture into small 1-inch meatballs and set aside on a plate.
In the slow cooker, pour in the chicken broth and sesame oil. Add shredded napa cabbage and shredded carrots. Stir to combine.
Carefully add the chicken meatballs into the slow cooker, spreading them evenly throughout the broth.
Cover and cook on low for 3 to 4 hours, or until the meatballs are cooked through and the vegetables are tender.
About 15 minutes before serving, whisk the two eggs in a small bowl until smooth.
In another small bowl, mix cornstarch and cold water until dissolved to create a slurry.
Slowly drizzle the whisked eggs into the slow cooker in a thin stream while gently stirring the soup to create delicate egg ribbons.
Stir in the cornstarch slurry to slightly thicken the broth. Continue cooking on low for 10 more minutes.
Add the baby spinach leaves to the slow cooker and stir until wilted, about 2 minutes.
Season the soup with salt and freshly ground black pepper to taste.
Ladle the soup into bowls and garnish with chopped fresh cilantro and chives before serving.