Heat the grill to high. Pat the trout dry using kitchen paper and put skin-side down on a baking tray. Sprinkle over a large pinch of fine sea salt and grill for 6-10 mins, depending on thickness, until crisp on top and cooked through.

Meanwhile, put the mustard, lemon juice, honey, 2 tbsp of the oil and most of the dill in a lidded jar and shake well to combine. Season well. Will keep for up to two days.

Heat the remaining oil in a large non-stick pan over a medium-high heat. Add the spring onions and capers and sizzle for 1-2 mins until slightly coloured. Mix in the grains, cook for 2 mins until heated through and season to taste. Serve alongside the trout with the watercress and remaining dill scattered over.