Preheat oven: Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish.

Sauté onion: In a medium skillet, melt the butter over medium heat. Add the chopped onion and cook until softened, about 5 minutes.

Combine ingredients: In a large bowl, combine the cooked macaroni, tuna, cream of mushroom soup, frozen peas, shredded cheddar cheese, sautéed onion, and bread crumbs.

Mix well: Stir the ingredients together until well combined.

Bake: Pour the mixture into the prepared baking dish and bake for 20-25 minutes, or until the casserole is bubbly and the cheese is melted.

Serve: Serve hot, accompanied by your favorite side dishes.

Tips:

For a creamier casserole, add a splash of milk or heavy cream to the mixture.

You can add other vegetables to your tuna casserole, such as carrots, celery, or bell peppers.

For a spicier casserole, add a pinch of cayenne pepper or a dash of hot sauce.

Serve with a side salad or a crusty bread.

Enjoy your comforting tuna casserole!