Preheat the Oven: Start by preheating your oven to 375°F (190°C). Grease a baking dish lightly with oil or non-stick spray.
Prepare the Ingredients: In a large mixing bowl, combine the drained tuna, chopped hard-boiled eggs, and chopped spring onions. Add the black pepper to taste and mix everything together.
Layer the Dish: Transfer the tuna mixture to the prepared baking dish and spread it out evenly. Layer the sliced tomatoes on top of the tuna mixture. Finish by sprinkling the grated cheese generously over the top.
Bake: Place the baking dish in the oven and bake for 20-25 minutes, or until the cheese is melted, bubbly, and slightly golden.
Serve: Once the dish is done baking, remove it from the oven and let it cool for a few minutes before serving. It’s perfect on its own or paired with a fresh salad or steamed vegetables.