Place whole chicken in an ovenproof baking dish that measures 12 inches in diameter. Truss the chicken legs with kitchen twine and tuck the wings under the body of the chicken.
In a bowl mix the olive oil, lemon juice and zest, oregano, salt, pepper, and cayenne pepper, if using. Mix until combined.
Rub the outside of the chicken with the olive oil marinade.
Roast the chicken for 50 minutes.
Orzo
Meanwhile, bring the chicken stock to a boil and add ½ teaspoon of dried oregano. Keep hot until you add the orzo to the roasting pan.
Once the chicken has roasted for about 50 minutes, sprinkle orzo around the base of the chicken and pour in boiling seasoned stock. Scatter the smashed garlic around the base and top with lemon slices that have their seeds removed.
Return to the oven and bake for 20 to 25 minutes, or until the pasta has absorbed the liquid and when checked with an instant-read thermometer, the chicken has reached 165°F in the thickest part of the breast.
Top the orzo with feta and stir in fresh chopped parsley. Serve from the baking dish family style.