In a large saucepan, heat oil and sauté the celery, carrots, and cooking onion with a pinch of salt and pepper. Stir until the vegetables just start to soften.
Add the chicken stock and bring to a boil. Reduce heat to low and simmer until vegetables are completely cooked. During that time, ladle out enough broth to dissolve ½ a chicken bouillon cube in a mug or small bowl. Return it back to the soup.
Add the green onions, noodles, chopped chicken and stir.Serve hot.