Heat a large straight-sided skillet over medium-high heat. Add the oil, garlic, fennel, onion, and pepper flakes to the skillet. Sprinkle with 1/2 teaspoon salt. Cook, stirring often, with a wooden spoon until the vegetables are soft and fragrant, about 5 minutes. Deglaze with the wine and stir, scraping up any bits form the bottom of the scraping. Add the tomatoes, water and capers. Bring to a simmer and reduce the heat to medium-low to maintain a gentle simmer for 10 minutes.
Meanwhile, sprinkle the filets with the remaining 1/2 teaspoon salt. Slide the fish filets into the broth and cover with a tight fitting lid. Cook until the fish is firm and opaque all the way through, 12 to 15 minutes. Remove the lid and spoon some of the sauce over the fish. Sprinkle with parsley, drizzle with extra-virgin olive oil and serve with plenty of crusty bread to soak up the broth.
Any white fish will work for this such as sole or halibut.