Combine the lime juice, olive oil, garlic, scallions, lime peel, black pepper, cayenne, chili powder, cumin, dry mustard, salt, and coriander into a paste.
Flatten the hens by pressing heavily on the breast, cracking the bone. Spread the paste evenly over the hens. Cover with plastic wrap and then weigh them down, using cans on a plate for instance. Marinate in the refrigerator for several hours, 24 hours if possible. (This flattening allows the hens to cook evenly.)
Option 1 - Grill: Place skin side next to heat and cook on a hot grill about 20 to 25 minutes per side, turning occasionally to prevent overbrowning, although a little dark flecking is pretty and tasty.
Option 2 - Roasting: Preheat the oven to 400°F. Grease or spray a shallow roasting pan with nonstick spray. Place the hens side by side, but not touching, in the prepared pan. Cook the hens, uncovered, until a meat thermometer measures 170°F, and the juices run clear, about 45 minutes. If you are using two pans, rotate them periodically to allow even browning.
The hens may be cooked up to a day ahead and refrigerated. Reheat under the broiler or in a hot oven.
Split the hens completely and place them on a serving platter, piled up in a circular pattern.