Preheat the broiler and cover the broiler pan with aluminum foil.
In a bowl, combine the vegetable oil, rice vinegar, mirin, 1 teaspoon of the sesame oil, the salt and red pepper flakes. Whisk to combine.
In a non-reactive shallow baking dish, arrange the fillets skin side down. Pour the vinaigrette over the fish, cover and refrigerate for 30 minutes.
Bring a large saucepan of salted water to a boil. Add the asparagus and cook until just tender, 1 1/2 to 3 minutes, depending upon their thickness. Drain and shock in an ice water bath. Drain and pat dry. In the saucepan, heat the remaining 1 1/2 teaspoons oil over medium-high heat. Add the asparagus and soy sauce and cook until warmed through, about 1 minute. Adjust the seasoning, to taste. Remove from the heat, toss with the sesame seeds, and keep warm.
Remove the fish from the marinade and place on the prepared broiler pan. Broil 5 to 6 inches from the heat source until just cooked through, about 5 minutes.
Serve with the asparagus, and garnish with cilantro.