In a saucepan, combine the soy sauce, vinegar, juice from the lemons, garlic, ginger and brown sugar. Cook at low heat for 5 minutes, making sure all the sugar has combined well.
Put the salmon in a dish; pour the sauce over, making sure that the bottom sides of each fillet are coated. Sprinkle the top with pepper.
Bake for 15-20 minutes until the fish flakes with a fork. Baste the fillets with sauce at least once.
Place on plates and drizzle with the remaining sauce. Use pineapple as a sweet garnish.