Preheat your oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish with butter or non-stick cooking spray.
Cook the egg noodles according to package directions in a large pot of salted boiling water until al dente, then drain well in a colander.
While the noodles cook, melt the butter in a large skillet over medium heat, then add the chopped onion and celery, sautéing for 5-7 minutes until softened and fragrant before stirring in the minced garlic for 30 seconds until aromatic.
In a large mixing bowl, combine the drained noodles, sautéed vegetable mixture, condensed soup, milk, thawed peas, flaked tuna, 1/2 cup of shredded cheddar cheese, salt, and pepper, stirring gently until everything is evenly incorporated and coated in the sauce.
Transfer the mixture to the prepared baking dish, spreading it into an even layer, then top evenly with the remaining 1/2 cup of cheddar cheese and the panko bread crumbs.
Bake uncovered for 25-30 minutes, or until the casserole is bubbly around the edges and the topping is golden brown and crisp.