On a baking tray, season the Nile perch medallions on both sides with half of the garlic, salt, pepper, and a few drops of lemon juice. Drizzle a tablespoon of olive oil over the fish. Allow it to marinate for 30 minutes.
Place the fish in a preheated oven at 180°C (approx. 350°F) and bake for 30 minutes.
Meanwhile, prepare the accompaniment. In a skillet, heat a tablespoon of olive oil and the remaining garlic. Add the mushrooms. Season with a pinch of salt and pepper. Stir and sauté until the water evaporates.
In another skillet, heat the remaining olive oil, add the spinach leaves, and season with salt. Cook until the spinach is tender and the water has evaporated. Finally, combine the mushrooms with the spinach and mix well.
In a small saucepan, melt the butter over medium heat. When the butter is hot, add the lemon juice and chopped parsley. Stir and turn off the heat.
Once the fish is cooked, remove it from the oven. Serve the fish on a bed of spinach and mushrooms, drizzled with the sauce.
