Preheat oven to 425*F. Pat potatoes dry with paper towels. Toss potatoes and mushrooms with 2 1/2 tablespoons oil, 2 tablespoons cheese, 2 teaspoons garlic, 2 teaspoons rosemary, 1/2 teaspoon salt and 1/4 teaspoon pepper. In 13x9-inch baking dish, arrange potatoes and mushrooms in one layer; top with remaining 2 tablespoons cheese. Bake 15 minutes or until potatoes are lightly browned; set aside.
Meanwhile, in large nonstick skillet over medium heat, heat remaining 1 1/2 tablespoons oil. Add chicken pieces. Season lightly with salt and pepper; sprinkle with remaining rosemary and garlic. Cook chicken 10 minutes each side, brown in 2 batches if necessary.
Arrange chicken on top of potato mixture; drizzle with any oil from skillet and return to oven. Bake 40 to 50 minutes longer or until chicken is no longer pink in center.