Preheat the oven to 400°F (200°C)
Pat the boneless leg of lamb dry
Trim excess fat if needed
Open and flatten the lamb if tied
Season generously with salt and black pepper
Rub with olive oil
Add garlic, rosemary, thyme, and lemon zest if desired
Tie the lamb into a compact roast with kitchen twine
Place on a rack in a roasting pan
Insert a meat thermometer into the thickest part
Roast for 15 minutes at 400°F (200°C)
Reduce oven temperature to 350°F (175°C)
Continue roasting until desired doneness is reached
Remove at 125°F to 130°F for medium-rare
Remove at 135°F to 140°F for medium
Rest the lamb for 15 to 20 minutes
Slice against the grain
Serve warm