Preheat oven to 425°F.

Whisk half the oil and all of the lemon juice in bowl. Season with salt and pepper.

Place halibut on a baking sheet. Brush with some of dressing.

Transfer fish to oven and bake until just opaque in center, about 12 minutes.

Meanwhile, cook quinoa according to package directions until tender but still firm; set aside.

Add remaining oil to a saucepan with the garlic. Sauté over medium heat 1 minute.

Add spinach and tomatoes. Stir to coat. Cover and remove from heat. Let stand 1 minute to wilt spinach.

Divide quinoa between plates. Top with halibut, spinach and tomatoes and remaining dressing.