Step 1

Position racks in upper and lower thirds of oven; preheat to 400 degrees F.

Step 2

Combine Brussels sprouts, fennel, 1 Tbsp. oil, and 1/4 tsp. each salt and pepper in a large bowl; toss to coat. Spread in a single layer on a large rimmed baking sheet. Bake, stirring occasionally, until tender, 20 to 25 minutes.

Step 3

Meanwhile, place halibut on another large rimmed baking sheet and top with half of the garlic and the remaining 1/4 tsp. each salt and pepper. Combine lemon juice and melted butter in a small bowl. Drizzle or brush half of the mixture over the fish. Bake until the fish is opaque and flakes easily with a fork, 12 to 15 minutes.

Step 4

Meanwhile, combine quinoa, the remaining 1 tsp. oil, sun-dried tomatoes, olives, and parsley (or fennel fronds) in a medium bowl.

Step 5

Add the remaining garlic to the lemon-butter mixture. Pour the mixture over the vegetables and bake for 1 minute more. Serve the halibut and vegetables alongside the quinoa mixture.