Prep the oven and pan. Heat the oven to 375°F (190°C). Grease a 9x13-inch baking dish with a little butter or oil.
Cook the pasta. Boil noodles in salted water until just al dente.
Drain and set aside. Don’t overcook—pasta will keep softening in the oven.
Sauté the vegetables. In a large skillet, warm olive oil and 2 tablespoons butter over medium heat. Add onion, celery, and carrots.
Cook 6–8 minutes until tender. Stir in garlic for 30 seconds.
Make the sauce. Sprinkle in flour and stir to coat the vegetables. Cook 1–2 minutes.
Slowly whisk in broth, then milk. Simmer until slightly thickened, 3–5 minutes.
Season and enrich. Stir in Dijon, thyme, paprika, salt, and pepper. Add cheese and let it melt into the sauce.
Taste and adjust seasoning.
Combine the base. In a large bowl, mix turkey, cooked pasta, peas, and the sauce. Fold gently so the noodles don’t break.
Fill the dish. Spread the mixture evenly in the prepared baking dish. Sprinkle extra cheese on top if you want a gooey finish.
Make the crunchy topping. Melt the remaining 2 tablespoons butter.
Toss with crushed crackers or panko and a pinch of salt and pepper.
Finish and bake. Scatter topping evenly over the casserole. Bake 20–25 minutes, until bubbling at the edges and golden on top.
Rest and serve. Let it sit 5–10 minutes so it sets. Garnish with fresh parsley and serve warm.