For the pesto: In a food processor fitted with the metal blade, combine cheese, lemon juice and garlic. Pulse until a coarse paste forms. Add mint and pistachios; pulse until mint is finely chopped. With the motor running, pour in oil through the feed tube and puree until smooth. Season to taste with salt and pepper.
Use immediately or transfer to an airtight container and refrigerate for up to 1 week.
For the lamb: Preheat hot water bath to 133F.
Using a sharp knife, trim all but a thin layer of fat from the racks. Rub 2 Tbsp. oil all over racks to coat.
Place each rack in a separate sous vide pouch and seal. Immerse in preheated hot water bath for 2 hours.
Remove pouches from hot water bath. Transfer to an ice bath and chill for 1 hour. Preheat a grill to high or heat a heavy-bottomed skillet over high heat.
Open pouches and slice racks into chops (each rack should yield 6 or 7 chops). Rub chops all over with remaining oil and season well with salt and pepper.
Place chops on grill or in skillet and sear for about 90 seconds per side or until just browned. Arrange chips on warm plates. Serve with pesto.