Put the chicken breasts on a chopping board, cover with clingfilm and bash with a rolling pin until they are about 1cm (½in) thick. Drizzle with 1 tbsp olive oil, season, then fry in a large frying pan over a medium heat for 10 minutes, turning until golden all over and cooked through, with no pink show when cut open. Remove from the heat, put on a plate and cover with foil. Heat the remaining olive oil in the pan, add the shallot and fry for 2-3 minutes or until softened slightly. Add the tom yum paste and fry for 1 minute. Add the coconut milk, lemon grass, hot chicken stock, lime zest and juice, and the sugar then simmer for 5 minutes. Add the sugar snaps and simmer for 1 minute more, then remove the lemon grass. Cook noodles according to the pack instructions, or heat in a non-metallic bowl covered with clingfilm in the microwave for 3 minutes. Divide between 4 bowls, pour over the coconut soup base. Slice the chicken breasts thickly on the diagonal.