Heat oil in a soup pot over medium heat. Heat another soup pot with the stock and saffron threads to steep.
To the first soup pot add onions, carrots and garlic, and season with salt and pepper. Cook to tender then add lemon zest and stir. Add the steeped saffron stock and bring to a simmer. Add asparagus, peas, chicken and noodles*; and cook about 5 minutes then remove from heat. Stir in lemon juice, herbs and serve.
*If making soup in advance, omit noodles and cook separately the night you want reheat soup!