Step 1Place 3 1/2 cups of cold water in a saucepan over high heat. Cover. Bring to the boil. Add the polenta. Reduce the heat to low and cook, stirring, for 5–7 minutes, or until polenta is thick. Cover to keep warm.
Step 2Meanwhile, heat 2 teaspoons of oil in a large, non-stick frying pan on medium-high heat. Sauté onion and garlic for 5 minutes, or until softened. Add tomatoes and capers, stirring, for 2 minutes,or until tomatoes start to soften. Fold in spinach leaves, stir through basil and transfer to a bowl.
Step 3Wipe pan clean. Heat 1 1/2 tablespoons of olive oil in the same pan over medium-high heat. Cook the fish fillets for 5 minutes, turning once, or until they are browned and cooked through. Transfer onto four serving plates. Season the fish with cracked black pepper and serve with polenta and the tomato mixture.