Preheat oven to 350 F. Lightly coat a large baking dish with cooking spray. Set aside.
Bring a large pot of lightly salted water to a boil. Add elbow pasta and cook according to package directions until al dente. Drain, rinse under cold water, and set aside.
Heat olive oil in a large skillet over medium-high heat. Add onion and saute for 3 minutes. Add spinach and cook for 2 more minutes, or until wilted. Add artichokes and continue to cook for 1 more minute. Remove from the skillet and set aside.
Melt the butter in the same skillet over medium heat. Whisk in flour until smooth. Gradually add the milk and chicken broth, whisking constantly until smooth. Stir over medium-high heat until sauce is slightly thickened. Lower the heat and stir in garlic powder, cheddar cheese, salt and pepper. Gently fold in spinach and artichoke mixture. Remove from heat. Taste and add more salt or pepper if needed.
Toss together cooked pasta, chicken and sauce. Pour into prepared baking dish. In a small bowl, stir together the bread crumbs, Parmesan and Italian seasoning. Sprinkle the mixture on top of the pasta dish.
Bake 20-25 minutes or until bubbling around the edges and topping is lightly browned. Let stand 5 minutes before serving.