01 - Set the oven temperature to 425°F.
02 - Pat lamb racks dry, then season all sides generously with salt and freshly ground black pepper.
03 - Combine rosemary, thyme, parsley, garlic, lemon zest, and olive oil in a small bowl; mix thoroughly.
04 - Brush the meaty surfaces of the lamb racks evenly with Dijon mustard.
05 - Press the herb mixture firmly over the mustard-coated sides of the lamb racks.
06 - Place lamb racks bone-side down on a foil-lined roasting pan or rimmed baking sheet.
07 - Cook in the preheated oven for 20 to 25 minutes to achieve medium-rare (internal temperature 130°F), or adjust to preferred doneness.
08 - Remove racks from oven, tent loosely with foil, and allow them to rest for 10 minutes before carving.
09 - Slice between the bones and serve immediately.