Preheat the oven to 425°F
Pat the boneless lamb leg dry
Trim excess fat if needed
Rub with olive oil
Season all over with salt and black pepper
Add garlic, rosemary, thyme, and oregano
Tie the lamb with kitchen twine if uneven
Place on a rack in a roasting pan
Roast for 20 minutes
Reduce oven temperature to 350°F
Continue roasting until desired doneness
Check internal temperature with a meat thermometer
Remove at 125°F for rare
Remove at 130°F for medium-rare
Remove at 140°F for medium
Rest the lamb for 15 to 20 minutes
Slice against the grain
Serve immediately