A trio of toppings—a lemony sesame seed sauce, a chunky nut-and-herb “pesto,” and sweet-tart pomegranate—boost the flavor and appearance of simple seared Arctic char, a fish from the same family as trout and salmon. You can chop the nuts and herbs in a food processor to save time, but process them separately so that the herbs won’t get bruised and mushy. I like serving this dish with a roasted carrot salad.