Red Snapper with Korean Miso Vinaigrette

Name: Red Snapper with Korean Miso Vinaigrette
Ingredients: 2 tablespoons doenjang (Korean fermented soybean paste, see Note); 2 tablespoons mayonnaise; 1 1/2 tablespoons finely chopped peeled fresh ginger; 1 tablespoon fresh lime juice; 1/2 cup canola oil; Kosher salt; Pepper; One 8-inch piece of kombu; 1 cup loosely packed bonito flakes; 1/2 pound parsnips, peeled and cut into 2-by-1/4 -inch matchsticks; 1 medium onion, cut through the core into 1/4-inch-thick wedges; Four 6-ounce skin-on red snapper fillets; Toasted white sesame seeds, shaved radishes and cilantro leaves, for garnish