Have ready a dish large enough to accommodate the lamb in a single layer. Place the coriander, dill, and fennel seeds in a spice grinder, and finely grind.
In a medium bowl, combine the ground spice mixture, garlic, rosemary, sage, mint, and olive oil. Spread the mixture on both sides of each lamb section. Place lamb in dish, and transfer to refrigerator. Marinate at least 3 hours or overnight.
Heat a grill or grill pan until medium hot. Season lamb with salt and pepper, and place lamb on grill. Cook until medium rare, 6 to 8 minutes per side.
Transfer lamb to a cutting board. Let meat stand 5 minutes. Slice, and serve.