Heat oil in a large saucepan or Dutch oven on medium heat. Add onions; cook until softened. Stir in tomato sauce and cumin. Cook, stirring, until the tomato sauce has slightly darkened and thickened, about 3 min. Stir in chicken and garlic; cook until chicken is white and opaque.
Add the chicken broth, 2 cups (500 mL) water, celery, spinach, carrots, parsley stems, thyme and pepper. Loosely cover and bring to a boil then reduce to a simmer. Add noodles. Cook, uncovered, 6 to 8 min. until noodles are tender.