In a container or zip-top bag, combine the vinegar, mirin, parsley, garlic and salmon. Marinate for 4-6 hours.
Preheat the oven to 400°F.
Place the scallions in a bowl, cover with soy sauce, and marinate for 20 minutes.
On one or two baking sheets, toss the turnips and potatoes with the olive oil and a big pinch of salt and pepper. Roast until crisp-tender, 15-20 minutes. Remove from the oven and toss with the thyme, chives and lemon juice on the baking sheet.
Remove the salmon from the marinade, discarding excess marinade, and place on a baking sheet, along with the marinated scallions. Roast for 12-15 minutes, until cooked through.
Add all of the ginger-miso sauce ingredients except the oil to a blender and purée until smooth. With the motor running, drizzle in the oil until emulsified. Season to taste.
To serve, divide the salmon fillets and vegetables between plates. Top with ginger-miso sauce.