Using a sharp knife, cut the salmon into slices. Place the slices of salmon in a shallow nonmetallic dish.
Mix together the soy sauce, tomato catsup, rice wine vinegar, sugar, and garlic.
Pour the mixture over the salmon, toss well, and leave to marinate for about 30 minutes.
Meanwhile, heat 3 tablespoons of the corn oil in a large preheated wok.
All the leeks to the wok and stir-fry over a medium high heat for about 10 minutes, or until the leeks become crispy and tender.
Using a draining spoon, carefully remove the leeks from the wok and transfer to warmed serving plates.
Add the remaining oil to the wok. Add the salmon and the marinade to the wok and cook for 2 minutes. Spoon over the looks, garnish, and serve immediately.