1) In a large pot heat both oils, then add diced onions, celery, minced garlic, lemon grass paste, chilli powder and red chilli flakes and cook until soft over medium heat for 5 minutes.
2) Add the broth, tomatoes, chicken, fish sauce, cilantro leaves and bring to a boil, simmer for 10 minutes
3) Add the noodles to the pot and cook according to package directions, mine took 5 minutes
4) Once the noodles are done, stir in spinach leaves and lime juice and take off the heat and serve.