Put two litres water in a saucepan, add salt and bring to a boil. Stir in oil and add the pasta. Cook for 10 to 12 minutes or until pasta is al dente. Drain and rinse under cold, running tap water. Drain.
Toss pasta in the extra corn oil, then turn out into a serving dish. Keep covered with cling film wrap.
In a clean frying pan, melt butter and fry garlic, lemon grass and mushrooms. Pan-fry for about 3 to 4 minutes. Add tom yam paste and water. Cover pan with a lid to simmer for a while. Add prawns, squids, mussels and capsicum. Mix in seasoning.
Pour sauce over pasta and serve immediately with a garnishing.