1. Stir together bread crumbs, parsley, mint, rosemary, salt, and pepper in a bowl, then drizzle with 2 1/2 tablespoons oil and toss until combined well.
2. Put oven rack in middle position and preheat to 400 degrees F.
3. Season lamb with salt and pepper. Heat remaining tablespoon oil in a large heavy skillet over moderately high heat until hot but not smoking, then brown lamb 1 rack at a time, turning once, about 4 minutes per rack. Transfer to a 13- by 9- by 2-inch roasting pan, arranging fatty sides up.
4. Spread fatty sides of each rack with 2 teaspoons mustard. Divide bread crumb mixture into 3 portions and pat each portion over mustard coating on each rack, gently pressing to adhere.
5. Roast lamb until thermometer inserted diagonally 2 inches into center (do not touch bone) registers 130 degrees F (for medium-rare), 20 to 25 minutes, and transfer to a cutting board. Let stand 10 minutes, then cut into chops.

Yield: 8 servings