Toast the hazelnuts in a dry skillet over medium heat for 4 to 5 minutes. Wrap in a kitchen towel and rub to remove most of the skins.
Toast the sesame seeds, cumin seeds, and coriander seeds for 2 to 3 minutes, until fragrant.
Combine the hazelnuts, toasted seeds, peppercorns, and salt in a food processor. Pulse until coarsely chopped, not a paste.
Pat the lamb chops dry and season with salt and pepper.
Heat the olive oil in a heavy skillet over high heat. Sear the chops for 2 to 3 minutes per side, until deeply browned and the internal temperature reaches 125°F (52°C) for rare or 130 to 135°F (54 to 57°C) for medium-rare.
Rest the chops for 3 minutes. Brush lightly with the mustard while still warm, then press the dukkah firmly onto both sides.
Serve immediately, while the crust is still crisp.