Heat oven to 375°F. Lightly grease a 9x13-inch baking dish.
Boil noodles in salted water until just shy of al dente, 1–2 minutes less than package. Drain well.
Warm olive oil and 2 tbsp butter in a large skillet over medium heat. Soften onion for 3–4 minutes.
Stir in garlic for 30 seconds. Sprinkle in flour and cook, stirring, for 1 minute.
Whisk in chicken broth, then milk. Simmer, whisking, until thickened and smooth, 3–5 minutes.
Season with Dijon, thyme, salt, and pepper. Remove from heat and fold in sour cream and half the cheddar.
Combine sauce with turkey, peas and carrots, and drained noodles. Spread mixture into the baking dish.
Toss panko with melted butter, Parmesan, and paprika. Sprinkle over casserole. Top with remaining cheddar.
Bake until bubbling and golden, 18–22 minutes. Rest 10 minutes, then finish with parsley and serve.