Cut the salmon fillet in half horizontally to obtain 2cm slices. Coat with 1/2 tbs olive oil.
Mix the mustard and lemon juice and slowly whisk in the remaining olive oil.
Add the parsley, mint dill, capers and anchovy fillet and season with sea salt and pepper.
Bring a pan of salted water to boil. Add the watercress to the boiling water and cook for 2 minutes. Drain and squeeze excess water from the watercress then cut into manageable pieces and portion onto 2 plates.
Cook the salmon in a non stick pan for a minute each side.
Serve the salmon on top of the watercress and spoon the salsa verde over the top.