How to Make It
Preheat oven to 425°F. Toss the squash with 1 tablespoon of the oil, ½ teaspoon of the salt, and ¼ teaspoon of the pepper. Place on a rimmed baking sheet and bake until golden and tender, about 25 minutes.
Meanwhile, pat the grouper fillets dry with paper towels and season with the remaining salt and pepper. Heat the remaining oil in a large ovenproof skillet over medium-high. Place the fillets in the skillet in a single layer; cook until the edges are lightly browned, 3 to 4 minutes. Place the skillet in oven with the squash; bake until the fish is opaque, 4 to 5 minutes.
Cook the butter in a small saucepan over medium until it begins to turn golden brown, 2 minutes. Stir in the raisins; cook 30 seconds. Pour the butter mixture into a small bowl and whisk in the vinegar. Toss with the squash.
Serve the grouper with the squash, sprinkled with the parsley.