Preheat the oven to 350°F (175°C).
Cook the egg noodles according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the drained tuna, cream of mushroom soup, milk, chopped onion, garlic powder, black pepper, salt, thawed peas, and shredded cheddar cheese. Mix well.
Add the cooked egg noodles to the tuna mixture and gently stir until everything is evenly combined.
Transfer the mixture into a 9×13 inch baking dish and spread it out evenly.
Bake uncovered in the preheated oven for 20 minutes.
Remove the casserole from the oven and sprinkle the French fried onions evenly over the top.
Return the casserole to the oven and bake for an additional 10 minutes, or until the onions are golden brown and crispy.
Remove from the oven and let it cool for 5 minutes before serving.