1. Preheat oven to 375 degrees. Lightly grease in 2 quart baking dish and set aside
2. Cook noodles according to package directions, removing when al dente. Drain,and set aside
3. Melt butter in a large skillet over medium heat. Add Celery, bell pepper, and onion and cook until onion is translucent, stirring frequently.
4. Stir in flour, salt and pepper. Slowly add milk and cook , stirring constantly until thick and bubbly. Stir in Dijon mustard.
5. Add tuna, peas, noodles, and cheddar cheese and fold into the sauce.
6. Pour mixture into the prepared dish.
7. Combine Panko, Parmesan cheese, smoked paprika parsley and melted butter in a small bowl and sprinkle over the top.
8. Bake casserole for 25-30 minutes, uncovered, or until heated through and golden brown on top. Let stand for a few minutes before serving.