For the crust: In a bowl, blend the panko, mustard seeds, coriander seeds and parsley together. Season with salt and pepper.
For the wash: In a second bowl, blend the mustard with 1/2 cup water, whisking well to blend.
For the sauce: Whisk the yogurt, sour cream, watercress, vinegar, mint and garlic in a bowl. To ensure the spices are blended, scrape the sides and whisk a second time. Hold at room temperature if using within 30 minutes, or refrigerate for future usage.
For the salmon: Coat the salmon with the wash, and then finish the top side (skin side) with the crust. Repeat the process with each fillet.
In medium saute pan over medium heat, coat the bottom of the pan with the oil. When warmed, add the crusted side of the salmon to the pan and cook, in batches, until golden brown, 2 to 3 minutes. Flip the fish and finish cooking until desired temperature. Remove from the pan.
Finally, sauce the plates with 2 ounces of the watercress/mint sauce. Top with the salmon and fresh herbs if desired.