Lemon-Garlic Broiled Flounder with Spinach

Flounder is quickly cooked in a hot broiler using this quick and easy fish recipe. Lemon juice, garlic, salt and pepper create a simple but flavorful seasoning that goes well with braised spinach.
Preheat the grill to high heat, cover the roasting pan with foil, and place the grill 2 inches away from the stove. In a small bowl, combine 3 tablespoons olive oil, lemon juice, and garlic; season with salt and pepper.Heat the remaining oil in a skillet over medium-high heat. Saute the onion until softened, 3 minutes. Add the frozen spinach, cover, and cook until thawed, about 8 minutes. Uncover, season with salt and pepper, and drizzle with 1/2 cup flavored olive oil. Cook for 4 minutes to drain any excess liquid. Remove from heat, cover and keep warm.Lightly drizzle a foil-lined baking dish with cooking spray. Place the flounder fillet on top and season with salt and pepper. Drizzle the fish with the remaining flavored butter and bake, uncovered, until opaque and lightly browned, about 6 minutes.Divide the spinach into 4 plates. Place the fish on a layer of spinach and serve hot, sprinkled with lemon zest if desired.