HELPFUL TIP:
Red mullets can be found in good fish markets. If you’re having a hard time finding this classic Mediterranean fish, you can substitute with 4 whole flounders or with salmon filets about the same weight. You’ll need 4 whole flounders or 4 filets. You can also sear the salmon separately in a frying pan with a little olive oil on high heat to give it some color and a nice crust before adding the tomato sauce to finish it.
In a large nonstick skillet, heat 2 tablespoons of olive oil over a medium-high heat and add the onion and celery. Cook for about 7 - 8 minutes, until translucent and soft. Add the garlic and stir. Add the wine and cook until reduced by half, about 2 minutes. Add the tomato puree and crushed red pepper, if using, and cook for 5 minutes more, until the sauce begins to thicken. Season to taste with salt and pepper.
Place the fish in the pan and cover. Cook over low to medium heat for about 12 - 15 minutes, or until the fish is fork tender and the sauce thickened. Gently stir in the olives and capers, if using, 5 minutes before removing from heat. Serve, garnished with chopped parsley.