Season fish with salt and pepper. Set aside.
Heat olive oil in a frying pan or skillet over medium-high heat.
Add onions and garlic.
Saute, stirring occasionally, for about 2-3 minutes or until the onions are soft.
Add anchovies. Saute, stirring, for about 2 minutes.
Add tomatoes and red chili powder(pepper) flakes.
Saute, stirring occasionally, for about 3 minutes.
Add white wine or water, olives, capers and oregano.
Stir to combine.
Arrange fish on top in a single layer.
Spoon the sauce over fish.
Simmer for about 6-10 minutes or until the fish turns opaque and cooked through.
Add butter. Garnish with chopped parsley.
Remove from heat. Drizzle with olive oil.
Serve with crusty bread, rice and couscous.