Begin by boiling a large pot of water over high heat. Add the egg noodles and cook according to the package instructions until they are al dente, usually about 6-8 minutes. Once cooked, drain the noodles and set them aside, allowing them to cool slightly while you prepare the sauce.

In a separate mixing bowl, combine the cream cheese, milk, onion powder, garlic powder, salt, and pepper. Use a hand mixer or whisk to blend the ingredients together until you achieve a smooth and creamy consistency.

In a large mixing bowl, gently fold the cooked egg noodles with the canned tuna and frozen peas. Pour the prepared sauce over the noodle mixture, and stir well until everything is evenly coated.

Pour the combined mixture into a greased slow cooker, spreading it out evenly. Sprinkle an even layer of shredded cheese on top.

Cover the slow cooker with its lid and set it to cook on low for 3-4 hours. You'll know it's done when the mixture is heated through and bubbling at the edges.

Once cooked, remove the lid and gently stir the casserole to mix in the melted cheese. Serve it warm straight from the slow cooker.