In a large rondeau pot add 3 tablespoons of olive oil over high heat and add the mushrooms to caramelize or well browned, which takes about 7-8 minutes stirring every 2 minutes or so.
Next, turn the heat down to medium and scrap the mushrooms to one side of the pan add 1 tablespoon of butter, shallots, garlic, and celery to the other side of the pan and sauté until lightly browned and starting to tenderize, which takes about 2 to 3 minutes.
Mix everything together and then deglaze with white wine and cook until the liquid is almost gone, which takes about 1 to 2 minutes.
Stir in the flour completely with the vegetables to create a roux and then pour in the milk and turn to high heat to activate the roux to help thicken up the sauce.
Once the sauce is thickened, which will almost immediately happen once it begins to boil, finish it with thyme, salt, and pepper and mix until combined. Turn the heat off and set aside.
Cook the pasta in a large pot of boiling water according to its instructions. Drain and run cold water over the noodles until cool and then set aside.
Season the tuna on both sides with salt and pepper and then sear in 2 tablespoons of olive oil over high heat for 3-4 minutes per side or until very browned on both sides and almost cooked through out.
Set the tuna aside on a cutting board, squeeze on some lemon juice and rest for 1 to 2 minutes before chopping the tuna into large 1” chunks. Set aside.
Add the cooked noodles to the rondeau pot with the mushroom sauce and then add in the cooked tuna and 1 cup of peas and mix until combined.
Transfer the mixture to a 13x9 casserole dish and flatten out.
Breadcrumbs: in a medium-size bowl mix together the breadcrumbs with melted butter and ¼ cup each of shredded cheddar cheeses.
Sprinkle on the 1 cup each of shredded cheddar cheese and then top off with breadcrumb-cheese topping and bake in the oven at 350° for 20-25 minutes or until lightly browned and cooked.
Suppose you like your tuna noodle casserole extra creamy, my recommendation is to place the casserole under the broiler for 4 to 7 minutes or just until the breadcrumbs are lightly toasted and the cheese is melted, instead of baking it in the oven. This procedure will allow for a very creamy casserole with a slightly toasted top.
Optionally garnish with chopped parsley and serve.
Notes
Make-Ahead: You can make this recipe up to 30 minutes ahead of time, just keep it warm covered in the oven at 200°.How to Store: Cover and store it in the refrigerator for 4-5 days. Cover and store in the freezer for up to 3 months. Thaw in the refrigerator for 1 day before reheating and serving.How to Reheat: Add the desired amount to a saucepan and cover with foil. Bake in the oven at 350° for 8-12 minutes or until hot.If fresh tuna is not available, you can use frozen tuna that has been thawed.Use 1 pound of canned drained tuna if frozen or fresh is not an option.Other noodle options are farfalle, penne, or macaroni.Tuna Casserole almost always gets dried out if there is not enough sauce. Feel free to add a cup of the hot leftover pasta water from cooking the noodles to help loosen up and moisten.You can just use yellow or just white cheddar cheese for this recipe.