Preheat BBQ to medium-high.
Pat lamb dry with kitchen paper and coat with herbs de Provence; season to taste with salt and pepper. Heat oil in a medium cast-iron skillet on the gas cooktop on the side burner; add lamb and brown on all sides for 5-7 minutes or until golden. Set aside to rest for 10 minutes.
In a medium bowl, mix pistachios, bread crumbs and garlic oil.
Combine Dijon mustard and honey; brush all over the lamb; press the pistachio mixture over the lamb, ensuring the mustard layer is covered.
Preheat BBQ to medium-low and set up for indirect cooking.
Place the lamb rack on the grill (away from the heat source) and close the lid.
After 20 minutes, wrap each bone with foil to prevent over-blackening. Continue cooking, with the lid on, for a further 15 minutes, or until the core temperature of the lamb reaches 50-52 Celcius when using a temperature probe.
Once the desired temperature is reached, remove from the heat, and rest for 5-7 minutes before slicing in 2 bone increments. Serve immediately.