Place the salmon piece or fillets skin-side up in a shallow ovenproof dish. Cook in the oven for 15 minutes.
Meanwhile gently melt the butter in a small saucepan. Remove from the heat and stir in the mustard and dill. Season to taste. Remove the salmon from the oven and arrange the scallops round it, baste with the mustard sauce.
Return to the oven for a further 5 minutes. Slice the salmon quite thickly and serve on top of the spinach rocket and spoon over the mustard butter.