Beat the lemongrass with a saucepan. Mash the garlic cloves with their peel. Cut the white and light green of the spring onions into 2 cm long pieces. Cut the chilli pepper into rings. Roughly dice the tomato. Chop the ginger with the skin into small pieces.
Heat 1 tablespoon of oil in a saucepan and simmer everything in it over a medium heat for 4-5 minutes. Pour in 800 ml of water and bring to the boil. Put the chicken breast and 1/2 teaspoon salt in the saucepan, cook gently for 40 minutes.
Cook rice noodles according to the instructions on the packet. Clean the carrots and cut into fine strips. Remove the meat from the broth. Pour the stock through a sieve into a second saucepan. Add the coconut milk and the carrots and cook for another 5 minutes. Remove the skin and bones from the meat, dice and heat in the soup.
Spread the pasta in bowls. Season the soup with lime juice and pour over the pasta. Sprinkle with chopped peanuts.