In large bowl stir together olives, capers, red onion, tomatoes, basil, 3 tbsp parsley and 1 C olive oil. Season with salt, fresh black pepper and red pepper flakes and let stand at room temperature for 30 minutes.
In large fry pan, heat 3T remaining olive oil until hot. Working in batches, season fillets with salt and pepper. Cook on one side until opaque, about 3 minutes, lowering heat if necessary to prevent burning. Turn fillets over and cook 3 minutes more. Transfer to platter and loosely cover with foil to keep warm. Cook remaining batches wiping pan clean between batches and starting with fresh oil for each batch.
Remove fish to a serving platter pour lemon juice into pan and swirl around to combine with pan juices. Drizzle over fish and garnish with tomato-olive mixture.