Put the green beans into a roasting tin or preferably a shallow ovenproof dish that you would want to serve from. Toss them with a little of the oil and some seasoning.
Brush the salmon fillets with oil, season, then set them on top of the beans. Roast for 12 minutes.
Heat the remaining oil in a frying pan. When it’s hot, add the breadcrumbs and fry briskly until golden, then add the garlic and cornichons and cook for another minute.
Take the pan off the heat and stir in the mustard , parsley and lemon zest, mixing together well.
When 2 minutes of cooking time remain, spoon the breadcrumb mixture on top of the salmon and return it to the oven. Squeeze the lemon juice over the top of the fish and serve.