Preheat the oven to 400 degrees.
In a food processor, chop the pistachios, thyme and rosemary. Add half of the olive oil, process to a coarse paste and season with salt and pepper.
Scrape half of the pistachio paste into a bowl and stir in the remaining olive oil. Reserve the other half of the pistachio paste to use to garnish the plates.
Coat the lamb with half of the pistachio paste that you have just stirred the olive oil into. Wrap the pancetta slices around the rack between the bones, leaving the bones exposed. Spread the rest of the pistachio paste which you added the olive oil to all over the pancetta and set the rack in a small roasting pan.
Roast the lamb for 40 minutes, or until an instant-read thermometer inserted in the thickest part of the lamb registers 130 degrees for medium rare.
Transfer the lamb to a cutting board and let rest for 5 minutes. Reserve the pan drippings.
Meanwhile, spoon 1 teaspoon of the rendered pancetta fat from the roasting pan into a skillet and heat until shimmering. Add the scallions and cook over high heat until browned, about 4 minutes.
Carve the lamb rack into four 2 chop servings and transfer to plates. Spoon some of the scallions over each section of chops and place a spoonful of the reserved pistachio paste on each plate.