Preheat the oven to 220 °C (428 °F) with top and bottom heat.
Coat a roasting dish with olive oil and place the cod fillets in it. Drizzle with olive oil and season with sea salt and freshly ground black pepper.
Halve the cocktail tomatoes and distribute them around the fillets. Top the fillets with basil leaves and sliced mozzarella, then sprinkle with grated parmesan and drizzle with olive oil.
Bake on the top shelf for 15-20 minutes until golden brown.