Best Tuna Noodle Casserole from Scratch

Preheat the oven to 350 degrees F (175 degrees C). Lightly oil an ovenproof skillet and an 8x12-inch casserole dish.

Place tuna in the prepared skillet and bake in the preheated oven until fish flakes easily with a fork, 8 to 10 minutes.

Fill a large saucepan with lightly salted water and bring to a rolling boil. Cook fettuccine at a boil until tender yet firm to the bite, about 8 minutes. Drain and set aside.

Remove tuna from the oven; leave oven on.

Meanwhile, melt 3 tablespoons butter in a saucepan over medium heat. Cook onion and mushrooms until softened, stirring occasionally, 5 to 7 minutes. Stir in flour until blended. Add milk, bouillon concentrate, adobo seasoning, and black pepper. Cook, stirring constantly, until mixture is slightly thickened, about 5 minutes more. Remove sauce from heat and stir in Parmesan cheese.

Place remaining butter in a medium-sized microwave-safe bowl and heat in the microwave until melted, about 30 seconds. Stir bread crumbs into melted butter and set aside.

Add cooked fettuccine and flaked tuna to the cheese sauce and toss to combine. Transfer noodle mixture to the prepared casserole dish and top with torn bread.

Bake in the hot oven until golden brown, about 20 minutes.