01 - Set oven temperature to 300°F (150°C).
02 - In a small bowl, combine olive oil or melted butter, minced garlic, thyme, rosemary if using, salt, black pepper, and lemon zest.
03 - Pat turkey breast dry. Loosen skin gently and spread half of the herb mixture underneath; rub remaining mixture evenly over the skin.
04 - Scatter onion, carrots, and celery evenly in a roasting pan to form a bed and pour in the chicken broth.
05 - Position turkey breast skin-side up on top of the vegetable bed.
06 - Roast uncovered for 1 hour 45 minutes to 2 hours, or until internal temperature registers 165°F (74°C) at the thickest part.
07 - Increase oven to 425°F (220°C) for the last 10 minutes to crisp the skin if desired.
08 - Remove from oven, tent loosely with foil, and allow to rest for 20 minutes before slicing.
09 - Strain pan juices and serve alongside the sliced turkey breast.