Lightly salt the fish and set aside, covered in the refrigerator until ready to use.

Heat the olive oil in a large skillet and sauté the onions over medium heat, stirring, until translucent, about 7 minutes. Add the garlic and stir for a minute. Add the tomatoes and bay leaf, bring to a boil, reduce heat to medium-low, and simmer for 10 minutes. Add the drained capers and simmer for a minute.

Add the fish, season with salt and pepper, cover and simmer until the fish is cooked through but still tender, about 15 to 20 minutes. Serve hot.