Cook noodles according to package directions. Drain and set aside. Meanwhile, combine bread crumbs and the 1 tablespoon of melted butter; set aside.

For Sauce, in a medium saucepan cook celery and onion in the 1/4 cup butter until tender. Stir in flour, salt, dry mustard, and black pepper. Add milk all at once; cook and stir until slightly thickened and bubbly. Combine sauce, tuna, cheese, roasted sweet pepper, and cooked noodles. Transfer to a 1 1/2 - quart casserole. Sprinkle with crumb mixture. Bake uncovered, in a 375? oven for 20 to 25 minutes or until bubbly and crumb topping is golden.