Preheat the oven to 400°F Combine the onion, garlic, tomato and herbs in a bowl with the wine.
Place the salmon in a bowl and pour over the marinade. Leave for 5 minutes.
Lay out 2 large sheets of baking parchment on a baking tray and put a piece of salmon in the centre of each. Spoon over the marinade and cover the fish with the paper to make a packet. Place in a dish and bake for 5 minutes. Open the pouch and serve.