Brush the salmon with a little vegetable oil and season with salt and pepper and cook for 8 minutes. Once cool enough to handle, flake into large pieces. Keep all the salmon juic-es.
Sweat the onion in the butter until tender and add the fish stock and diced potato and simmer until the potato is just cooked.
Add the mixed vegetables, flaked salmon and all the salmon juices, and simmer for 2 minutes.
