Snapper Escabèche with Charred Scallions

Prepare grill for medium-high heat; oil grate. Combine onion, vinegar, and 6 tablespoons oil in a small bowl; season with salt and pepper. Set marinade aside. Rub snapper all over with 1 tablespoon oil total; season with salt and pepper. Grill, skin side down, until lightly charred and almost cooked through, 4 –6 minutes (skin should release easily; if it sticks, grill another minute or two). Turn; grill until just cooked through, about 1 minute. Place skin side up in a baking dish. Pour reserved marinade over hot snapper and let sit at least 10 minutes (the longer it sits, the more intensely flavored it will be). Meanwhile, toss scallions on a baking sheet with remaining 1 tablespoon oil; season with salt and pepper. Grill, turning often, until lightly charred and wilted, about 2 minutes. Transfer to a cutting board. Let cool; coarsely chop. To serve, spoon marinade over snapper and top with scallions and parsley.