Preheat oven to 375°F. Place chicken in 13x9-inch baking pan coated with no stick cooking spray. Mix 1 tablespoon each of the oil and rosemary and 1/2 teaspoon of the garlic salt; rub all over chicken.
Sprinkle 1/2 tablespoon of the rosemary inside chicken cavity. Squeeze juice of 1/2 lemon over chicken; place squeezed lemon half inside cavity.
Mix potatoes, onions, pepper, remaining 1 1/2 tablespoons rosemary, remaining 1 tablespoon olive oil, remaining 1/2 teaspoon garlic salt and juice of remaining 1/2 lemon in large bowl. Arrange mixture around chicken.
Roast 1 1/4 to 1 1/2 hours or until chicken is cooked through and potatoes are tender.