Step 1: Make the herb paste. Place the garlic, herbs, salt, peppercorns, and lemon zest in a mortar, and using the pestle, pound them to a coarse paste. Gradually work in the olive oil and pound to a smooth paste. Alternatively, place the garlic, herbs, salt, peppercorns, and lemon zest in a food processor and finely chop. Add enough olive oil to process to a smooth paste, scraping down the side of the bowl with a rubber spatula.
Step 2: Using the tip of a paring knife, make small slits on all sides of the roast, about 1/2 inch deep and 1-1/2 inches apart. Using the tip of your index finger, widen the holes. Place a tiny spoonful of herb paste in each hole, forcing it in with your finger; this will use up about half of the herb paste. Spread the remaining herb paste over the roast on all sides. You can cook the roast right away, but it will have even more flavor if you let it marinate in the refrigerator, covered, for 1 to 2 hours.
Step 3: When ready to cook, place the drip pan in the bottom of the rotisserie. Skewer the roast by inserting the spit between the ribs. Tighten the prongs. Attach the spit to the rotisserie and turn on the motor. If your rotisserie has a temperature control, set it to 400 degrees. If using a grill, preheat it to medium high.
Step 4: Cook the roast until it is darkly browned on all sides and cooked to taste, 1-1/4 to 1-1/2 hours for medium-rare (145°F). Use an instant-read meat thermometer to test for doneness; don’t let the thermometer touch the spit or a bone.
Step 5: Transfer the roast to a platter or cutting board, remove the spit, and let the meat rest for about 10 minutes. Reserve the drippings for the sauce. To carve, cut the meat off the ribs, running your knife along the inside of the bones. Cut the two ribs apart. Thinly slice the roast crosswise and serve.