In medium skillet, heat oil over medium-high heat; add mushrooms, Italian seasoning and garlic powder. Salt and pepper to taste; sauté until softened and slightly browned. Set aside.
Salt and pepper chicken breasts; place in an 11x7-inch baking dish. In medium bowl, combine mushrooms, artichokes, mayonnaise and sour cream; pour over chicken.
Bake in a preheated 375°F oven 30 minutes or until chicken reaches 170°F on an instant read thermometer.