Bring a pot of salted water to a rapid boil. Cook the asparagus for 1 minute, remove from the pot with a strainer and rinse under cold water; drain and set aside. Cook the noodles in the same salted water two minutes less than the package directions. Drain noodles and add to a large mixing bowl. Melt the butter in a saucepan, and sauté the onions over medium low heat for about 3 to 5 minutes. Add the garlic and flour, and continue cooking, stirring, for another 2 minutes. Whisk in the milk, mushrooms, salt, and pepper; cook this mixture stirring, until the mixture begins to simmer and thicken. Add the cooked sauce to the bowl of noodles. Add the chicken, asparagus and half of the cheese; mix with a spatula to combine. Pour the mixture into an 11 x 14 inch casserole dish, and top with the rest of the cheese. Mix the breadcrumbs and olive oil until combined and spread evenly over the casserole. Bake for 35 to 45 minutes at 350° F until bubbling and browned. Makes 8 servings.