Bring a large pot of salted water to a boil. Add egg noodles and cook according to package directions until al dente. Drain and set aside.
In a skillet over medium heat, melt butter. Add diced onion and cook until soft, about 5 minutes. Stir in garlic and cook for 1 minute.
Sprinkle flour over the onions and garlic. Stir constantly for 2 minutes to combine.
Slowly pour in milk and chicken broth, whisking to prevent lumps.
Stir in garlic powder, onion powder, salt, and pepper. Keep cooking, stirring often, until the sauce thickens, about 5 minutes.
Stir in drained tuna and frozen peas. Cook for 2-5 minutes until heated through.
Add the cooked noodles into the skillet and stir well.
Stir in shredded cheddar cheese until it melts and combines smoothly.
Taste and adjust seasoning if needed. Serve warm, garnished with parsley.