Mix butter, garlic, thyme, rosemary, lemon zest, 1/2 teaspoon salt, and 1/2 teaspoon pepper together in a bowl.
Loosen skin on chicken breast; rub butter mixture between skin and breast meat. Press on the skin to distribute evenly. Rub oil, remaining 1/2 teaspoon salt, and 1/2 teaspoon pepper all over; place lemon halves inside cavity. Set in a baking pan.
Roast in the preheated oven, basting after 30 minutes, until chicken is no longer pink, about 1 hour. An instant-read thermometer inserted into the thickest part of the thigh, near the bone, should read 165 degrees F (74 degrees C). Let rest before carving, about 15 minutes.
