How to Make It
Preheat the oven to 425°. Put the halibut in a large shallow dish and rub the steaks all over with the olive oil and thyme. Let stand at room temperature for 30 minutes.
In a large bowl, whisk the melted butter with the sake, mirin, soy sauce and miso until combined. Add the sweet potatoes and toss to coat. Spread the sweet potatoes on a large rimmed nonstick baking sheet and roast them for 35 minutes, turning once, until tender and lightly browned.
Shortly before serving, heat a cast-iron grill pan until almost smoking. Season the halibut steaks with salt and pepper and grill, turning once, until they are just cooked through, about 7 minutes. Toss the sweet potatoes with the lime juice and parsley leaves. Set the halibut steaks on plates and top with the Five-Vegetable Slaw. Spoon the sweet potatoes alongside and serve immediately.