Step 1

Preheat oven to 425°. Toss fennel, onion, potatoes, and oil in a 3-qt. baking dish to coat; season with salt. Roast, tossing once, until vegetables are browned and softened, 35–40 minutes.

Step 2

Meanwhile, melt butter in a small saucepan over medium heat. Mix in garlic, ginger, curry powder, and a pinch of salt. Simmer until color intensifies, about 1 minute. Remove from heat.

Step 3

Season fish with salt and lay on top of cooked vegetables. Drizzle fish with curry butter. Reduce oven temperature to 350° and bake fish until flesh easily flakes apart with a fork, 12–15 minutes.

Step 4

Serve vegetables and fish with mint scattered over.