01 - Bring a large pot of salted water to a boil. Cook pasta according to package directions until al dente. Drain and set aside.
02 - In a large bowl, mix cooked pasta, drained tuna, cream of mushroom soup, frozen peas, and half of the shredded cheese until evenly incorporated.
03 - Transfer the mixture into a lightly greased baking dish. Spread evenly and top with the remaining cheese.
04 - Preheat oven to 375°F (190°C). Bake the pasta gratin for 20 minutes or until the cheese is melted and the top is lightly golden.
05 - Let rest for 5 minutes before serving warm.