Season cod fillets on both sides with salt and pepper; set aside.
In a large skillet over medium heat, add oil. When hot, add onion and sauté for 2 minutes.
Add anchovies including the oil from the can, red pepper flakes, olives and capers; stir and cook for 2 minutes.
Add garlic and sauté for 30 seconds. Add wine and simmer for 2 minutes.
Add tomatoes and season with salt and pepper. Cook for 8 minutes but 2 minutes before time is up, add Italian seasoning; cook for the remaining time.
Add seasoned cod and spoon sauce over. Cover, reduce heat to medium-low, and, depending on the thickness, simmer for 12 to 15 minutes. Spoon more sauce halfway through cooking.