russet potatoes, peeled and cut into 1/2-inch-thick rounds
olive oil, plus more for the grill
kosher salt and black pepper
6-ounce pieces halibut, cod, or striped bass fillet
large red onion, sliced into 1/2-inch-thick rings
fresh lemon juice, plus lemon wedges for serving
- Heat grill to medium-high. Divide the potatoes between 2 large pieces of heavy-duty foil and, dividing evenly, toss with the vinegar, 1 tablespoon of the oil, and ½ teaspoon each salt and pepper. Fold the foil over the potatoes and seal the edges to form 2 packets. Place on grill and cook, turning once, until the potatoes are tender, 20 to 25 minutes.
- Meanwhile, rub the halibut and onion with the remaining tablespoon of oil and season with ¼ teaspoon each salt and pepper. After the potatoes have cooked for 15 minutes, oil grill. Add the halibut and onion and cook until the halibut is opaque throughout, 3 to 5 minutes per side, and the onion is tender, 4 to 5 minutes per side.
- In a small bowl, toss the arugula with the lemon juice. Top the halibut with the arugula and serve with the potatoes, onion, and lemon wedges.