Preheat the oven to 375F. In a small saucepan, heat the 1/2 cup of balsamic vinegar until reduced to 3 tablespoons. Once cool, stir in 1 tablespoon of the canola oil and set aside. 

Heat a grill pan over medium high heat. Grill corn until charred all over, turning frequently so it cooks evenly. Let cool, and with a sharp knife cut the kernels from the cobs.

Slice and portion out approx 6 oz. filets of salmon. Using the tip of a sharp knife, make five 1/2-inch-deep slits crosswise in the flesh of each fillet. Stuff 1 slice of ginger into each slit, then thread each fillet lengthwise with a short skewer, securing the ginger.

In a large, ovenproof nonstick skillet, heat 1 tablespoon of canola oil. Season salmon fillets with salt and pepper and then place in skillet, skin side down. (you may have to cook in batches depending on the size of your skillet) 

Cook over moderately high heat until the skin is crisp, about 3-4 minutes. Turn salmon and transfer skillet to the oven and roast for another 5-6 minutes, until no longer translucent and remove. 

In a large bowl, whisk the remaining 2 tablespoons of balsamic vinegar with the mustard and honey. Then whisk the remaining 1/4 cup of canola oil into the dressing.

Add the grilled corn kernels and watercress to the bowl and toss to coat. Transfer the salad to plates and top with the skewered salmon. Drizzle the fish and salad with the balsamic vinegar reduction and serve immediately.