Preheat the oven to 375 degrees and lightly grease a 9x13 baking dish.
Bring a large pot of water to a boil and cook the elbow macaroni according to package directions until just tender. Drain and return the pasta to the pot.
Add the drained tuna, frozen peas, 1.5 cups of the shredded cheddar cheese, milk, salt, and pepper to the pot with the pasta.
Stir everything together until the cheese begins to melt and the ingredients are evenly coated.
Transfer the mixture to the prepared baking dish and spread it into an even layer.
Sprinkle the remaining 1/2 cup of cheddar cheese over the top.
Bake for 20 minutes until the cheese is melted and the edges are lightly golden.