In a heavy-bottomed casserole, heat 3/4 of the oil over medium-high heat. Add the onion, pearl onions, bay leaf, and garlic. Cook, stirring, for 5 minutes.
Cook a few more minutes, stirring constantly, then add the red wine, and cook 5 minutes, continuing to stir constantly. Add the tomato sauce, pepper puree, and white wine. Season with salt and pepper, bring to a boil, then reduce to a simmer, and cook for 10 minutes.
Add the fish and simmer until it's opaque, about 5 minutes. Remove the onion and add the remaining tablespoon olive oil. Sprinkle the parsley and divide evenly among 6 warmed bowls.