Preheat the broiler to high heat and position an oven rack in the upper third of the oven.
Meanwhile, in a large mixing bowl, combine the cooked pasta, olive oil, flaked cooked cod, tomatoes, bell pepper, olives, and some salt and pepper to taste; thoroughly stir to combine.
Grease a rectangular baking dish with olive oil. Transfer the cod-pasta mixture to the baking dish, spreading it out evenly. Scatter the mozzarella on top.
Place the baking dish under the broiler; cook until the cheese is bubbling and golden brown, 3-4 minutes.
Remove from the oven and let cool for a few minutes before serving.
