Preheat the oven to 425°F. In a large skillet over medium heat, preheat the olive oil. Add onion, garlic, and red pepper flakes. Cook until golden, stirring occasionally. Add fennel and cook until translucent.
Reduce to medium heat, add tomatoes and cook for 5 minutes. Add 1 sprig of chopped basil, wine, and olives. Season with salt and pepper to taste.
Reduce to low and simmer until the sauce is slightly thickened.
Meanwhile, pat the fillets dry, lightly spray them with cooking spray and season with salt and pepper.
In an ovenproof skillet over high heat, heat the olive oil until shimmering. Add the fillets and cook for 2 minutes. Flip the fillets and place the skillet in the oven. Bake until the fish is no longer translucent.
Switch the oven to broil and place the skillet on the upper rack. Broil until the tops of the fillets are golden brown.
On a serving plate add the sauce and the fish on top. Enjoy!