Heat a wok and coat with vegetable oil. Add shallot and saute until it begins to turn brown. Add ginger, chilies, lemon grass and lime and saute until fragrant. Add fish sauce and scrape up any brown bits. Add chicken stock, reduce heat and simmer for 20 minutes. Through a fine sieve into a saucepan, strain out solids. Bring broth back to a boil and add shrimp and enoki mushrooms. Cook until shrimp turn pink. Season and drop cilantro sprigs in soup be