02Add the mushrooms, lemon grass pieces and tomato. Bring to a boil, reduce the heat to medium and simmer for 4 minutes. Add the shrimp and simmer until they are opaque, about 2 minutes. Pour into a tureen. Stir in the scallion, bean sprouts, lime zest and juice, pepper, fish sauce, chili flakes and chili oil. Serve with the rice.