Preheat the oven to 450°F.

In a small bowl, stir together herbes de Provence, mustard, 1 1/2 teaspoons of the salt, onion powder, pepper, paprika and 1 1/2 tablespoons of the oil.

Rub mixture all over lamb and place on a rack set inside a roasting pan.

Roast until golden brown and sizzling, about 30 minutes.

Lower oven temperature to 350°F and continue to roast, basting lamb with pan juices once or twice, until done to your liking, 1 1/4 to 1 1/2 hours more for medium (an instant-read thermometer inserted into thickest part of meat, without touching bone, will register 145°F).

Transfer lamb to a cutting board and let rest for 15 minutes.

Meanwhile, combine olives, parsley, anchovies, orange zest and juice, and remaining 1/2 teaspoon salt and 1 tablespoon oil in a food processor and pulse until roughly chopped.

Carve lamb into slices and serve warm, topped with olive tapenade.