Preheat the oven to 325°F to 350°F
Pat the lamb thigh dry with paper towels
Season generously with salt, pepper, garlic, rosemary, and thyme
Rub with olive oil
Optional: marinate for several hours or overnight
Place the lamb in a roasting pan or baking dish
Add onions, garlic, or vegetables if desired
Roast uncovered until browned
Cook until the internal temperature reaches 145°F for medium-rare or 160°F for medium
Baste occasionally with pan juices if desired
Remove from the oven and rest for 15 to 20 minutes
Slice against the grain
Serve with the pan juices or sauce