While you’re frying the third batch, heat up a pan and add a few tablespoons vegetable oil. Sauté the onion, garlic and ginger until soft. Add the celery and stir, add chicken stock and the sauce. Bring to a boil. To make the sauce a little thicker, add slurry of 1/2 tsp cornstarch mixed with a tbsp cold water. Bring to just a boil and turn off heat. Taste and add more chili sauce if you like. Put the chicken in and mix. Finally, add the scallions and cilantro. Serve immediately.