Step 1

Whisk together the mustards, honey, horseradish, mint and 1/4 teaspoon of salt and 1/4 teaspoon of pepper in a small bowl. Let sit for at least 15 minutes before using. Can be made 1 day in advance and refrigerated but do not add the mint until just before using. Bring to room temperature before using.

Step 2

Heat the grill to high.

Step 3

Brush the salmon with the oil and season with salt and pepper. Place the salmon on the grill, skin side down, and grill until golden brown and slightly charred, about 3 minutes.

Step 4

While the salmon is cooking, place the watercress and onion in a medium bowl, add the vinegar and oil and salt and pepper and toss to combine. Transfer the salad to a platter, top with the salmon fillet and drizzle each fillet with the mustard sauce.