Gingered Salmon with Grilled Corn and Watercress Salad

plus 2 tablespoons balsamic vinegar

plus 2 tablespoons canola oil

small ears of corn, shucked

skin-on salmon fillets

small slices of pickled ginger (about 1 ounce)

Salt and freshly ground pepper

Dijon mustard

honey

bunch of watercress, thick stems discarded (about 8 ounces)