If you have seasoned bread crumbs instead of panko, you can use them instead. Slideshow: Best Noodle Dishes
Preheat the oven to 350°F. In a medium heavy saucepan, heat 3 tablespoons of the butter over medium high heat until hot, then whisk in the flour and cook, 1 minute. Whisk in the milk and bring to a simmer, whisking. Boil the milk mixture, whisking occasionally, 10 minutes. Remove from the heat and whisk in the cheese. Season with salt and pepper to taste.
Pour boiling salted water over the ramen and let stand 5 minutes, then drain. Stir the noodles and the chicken into the sauce. Place the chicken-noodle mixture in a buttered 3-quart baking dish.
Melt the remaining 2 tablespoons of the butter and toss with the panko. Spread the panko evenly over the casserole. Bake the casserole until golden and bubbling, about 30 minutes. Let cool slightly, then serve.