Divide leg of lamb into four large pieces by slicing along areas (“seams”) where the leg naturally separates. Trim away and discard excess fat and sinew.
Rub all surfaces of the lamb pieces with the olive oil and season generously with French Provencial Salt. Allow meat to rest, at room temperature, for at least one hour before cooking.
Prepare your grill for cooking on high heat. Grill all lamb pieces at once, turning often, until outside of meat is lightly charred and an instant-read thermometer, inserted in the thickest part, registers 130°F, about 25 min.
On reaching target temperature, immediately remove from the grill and transfer cooked lamb pieces to a cutting board. Allow meat to rest 10 minutes before slicing, thinly, against the grain. Serve with anchovy mayonnaise or garlic aioli.
Do ahead: Lamb can be seasoned 2 days ahead. Cover and chill.
Adapted from Epicurious.