Whisk together Greek seasoning, lemon juice, and 2 tablespoons olive oil in a small bowl.
Loosen skin from chicken breasts and drumsticks without totally detaching skin.
Rub Greek seasoning mixture evenly under skin.
Arrange 3 lemon slices on each side of breast under skin; carefully replace skin.
Place remaining lemon slices and next 3 ingredients into chicken cavity.
Tie ends of legs together with string; tuck wing tips under.
Place chicken, breast side up, on a lightly greased rack in a lightly greased shallow roasting pan.
Lightly coat chicken with cooking spray; sprinkle evenly with 1 teaspoon salt and ¼ teaspoon pepper.
Bake at 450° for 30 minutes.
Stir together new potatoes, rosemary, and remaining 1 tablespoon oil, ¼ teaspoon salt, and ¼ teaspoon pepper in a bowl.
Remove chicken from oven; pour 2 cups chicken broth over chicken.
Arrange potato mixture in a single layer on wire rack around chicken; return to oven.
Reduce oven temperature to 400°.
Bake at 400° for 40 minutes or until meat thermometer inserted into thigh registers 175°, basting every 15 minutes with pan juices.
Cover loosely with aluminum foil to prevent excessive browning, if necessary.
Remove from oven, and let stand 10 minutes before carving.
Serve chicken and potatoes on fresh spinach leaves drizzled with pan juices, if desired.
(The hot pan juices will wilt the spinach.
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