Preheat the oven to 425°F. Bring a large pot of salted water to a boil and cook the egg noodles per the package's instructions, until they are 2 minutes shy of al dente (mine cook for 4 minutes). Drain well, and add to a 13x9 pan. Add the frozen peas to the hot noodles and set aside.

In the same pot you boiled the noodles, melt the butter over medium-high heat. Add the diced celery and onion and cook, stirring occasionally, until softened, 6 to 8 minutes.

Turn the heat down to low and add the soup, drained tuna, milk, salt, pepper, and garlic powder to the pot with the vegetables. Stir until fully combined.

Turn the heat back up and bring the mixture to a boil. Once boiling, remove the pot from the heat.

Pour the hot tuna mixture over the noodles and stir until everything is evenly coated.

Sprinkle the Ritz cracker pieces evenly over the top, then sprinkle on the shredded cheddar cheese.

Bake at 425°F for 15 to 20 minutes, until the top is golden brown and the casserole is bubbling around the edges.

Remove from the oven and let the casserole rest for 5 to 10 minutes before serving.