Season fillets with salt and freshly ground pepper to taste. Drizzle with lemon juice and 1 tbsp of the oil.
In a large nonstick skillet heat 1 tbsp oil over medium heat. Add fillets and cook 5 – 7 minutes per side or until fish flakes easily with a fork. Add capers, and sprinkle fillets with red pepper flakes. Reduce heat to low and keep warm.
In another large nonstick skillet heat remaining oil over medium heat. Add spinach in batches and cook, stirring, until wilted. Transfer to a colander to drain.
Return skillet to medium heat. Add tomatoes and cook 2 minutes. Place spinach on a serving platter, place fillets on spinach, top with tomatoes and serve.