Bring a large pot of salted water to a boil.
Cook your egg noodles for **2 minutes less** than the package instructions indicate
While the noodles cook, melt butter in a large oven-safe skillet or saucepan over medium heat.
Add the diced onion. Cook for about 4-5 minutes until they soften and turn translucent.
Add the mushrooms and cook for another 3-4 minutes until they release their moisture and start to turn golden
Add the flour directly to the vegetable mixture and stir constantly for 1-2 minutes
Now slowly pour in the milk, a little at a time, whisking constantly
Season with freshly cracked black pepper and Dijoin mustard and whisk until well incorporated.
Add in the chicken broth and continuing to whisk until everything is mixed together.
Remove the pan from the heat before adding the cheese. Stir in the shredded cheddar off the heat and watch it melt beautifully into the sauce.
Drain the tuna over a sieve
Pasta noodles should are done and al-dente, drain and leave it in the pan.
Add the creamy sauce to the pasta.
Add the drained tuna, and frozen peas directly into the pasta and sauce
Stir gently until everything is evenly coated and well mixed. Everything should be well incorporated.
Transfer the mixture to baking dish
In a bowl mix together panko breadcrumbs, melted butter/oil, paprika, and salt. Mix together until every crumb is coated.
Spread cheese evenly over the top of the casserole in a single layer.
Spread the panko mixture evenly over the top of the casserole in a single layer.
Bake at **375°F (190°C) for 25-30 minutes until the sauce bubbles around the edges and the topping is a deep golden brown
Once baked, let the casserole rest for 5 minutes before serving
Garnish with fresh parsley and enjoy
