1. Pour the ingredients needed for the marinade into a blender. Blend until smooth, then pour the marinade into a bowl. Add the lamb, turning to coat evenly. Cover and refrigerate for 4 to 6 hours.

2. Remove the lamb from the container and set the marinade aside. Pour the marinade into a saucepan, bring to a boil, and let boil for a good minute. Remove from heat and set aside.

3. Roll the lamb leg and tie it with kitchen twine. Thread the lamb leg lengthwise and center it on the spit. Secure the spit on the rotisserie and cook the lamb on the barbecue with indirect heat, lid closed, for 60 to 90 minutes, until the internal temperature reaches 62°C for medium-rare meat, basting with the reserved marinade every 20 minutes. Stop the rotisserie. Put on barbecue gloves and carefully remove the spit from the rotisserie to place it on a cutting board. Remove the spit and let the meat rest for 20 minutes before slicing.

4. Reheat the beans in a saucepan over medium heat. Add the tomatoes, olives, oil, parsley, vinegar, and mix vigorously. Season to taste. Serve hot with the lamb slices.