Preheat oven to 350°. Cook pasta according to package directions; drain., In a large skillet, heat butter over medium-high heat; saute mushrooms and onion until tender. Remove from heat., In a large bowl, whisk together eggs, milk and seasonings. Stir in chicken, artichoke hearts, spinach, cheeses and mushroom mixture. Stir in pasta., Transfer to a greased 13x9-in. baking dish. Bake, covered, 40 minutes. , Mix topping ingredients; sprinkle over casserole. Bake, uncovered, until bubbly and topping is golden brown, 5-10 minutes.