Place a large nonstick skillet over medium-high heat until hot. Sprinkle chicken on both sides with 1 tablespoon Greek seasoning; coat with cooking spray. Add chicken to skillet; cook 2 minutes on each side or until browned. Transfer chicken to a 2-quart baking dish; set aside.
Coat mushrooms and artichoke hearts with cooking spray; add to skillet. Cook, stirring constantly, 2 minutes or until mushrooms are tender; stir into chicken in baking dish.
Combine 1 cup chicken broth, sherry, salt, and remaining 1 1/2 teaspoons Greek seasoning in skillet; bring to a boil. Combine remaining 1/3 cup broth and flour, stirring with a whisk until smooth. Stir flour mixture into sherry mixture. Cook 1 minute or until thickened; pour over chicken mixture.
Cover and bake at 375° for 35 minutes.