4 garlic cloves, smashed and peeled
2 cups packed cilantro leaves
2 cups packed parsley leaves
2 tablespoons coarsely chopped preserved lemon, or 2 teaspoons grated lemon zest
1/2 cup extra-virgin olive oil
1/4 cup preserved lemon juice, or 1/3 cup fresh lemon juice
2 teaspoons ground cumin
1 teaspoon kosher salt
1 teaspoon sweet paprika
1/4 to 1/2 teaspoon crushed chile flakes
3 pounds American leg of lamb, trimmed and cut into 1 1/2-inch cubes
12 to 16 metal skewers, or wooden skewers soaked in water for at least 30 minutes
1 bunch green onions, trimmed and cut into 1 1/2-inch segments
2 pounds heirloom tomatoes in a variety of colors and sizes, cut into thick slices or quartered
To make the Charmoula Sauce: In a food processor (or with a knife), finely mince the garlic, stopping to scrap down the sides of the bowl as needed. Add the cilantro, parsley, and preserved lemon or zest and pulse until all ingredients are finely chopped.
Transfer the mixture to a bowl and stir in the olive oil, lemon juice, cumin, salt, paprika, and chile flakes. Taste and adjust the seasoning. (The sauce can be covered and refrigerated for up to 2 days. There should be enough oil to cover the surface to preserve the herbs; if not, top with a bit more.)
Coat the lamb in about half of the charmoula sauce and marinate at least 1 hour or overnight. (Refrigerate if marinating for more than 2 hours.)
Prepare a hot fire in a charcoal or gas grill. Thread the meat onto skewers, dividing it evenly and alternating with a piece of green onion between each cube.
Grease the grill grates with oil. Place the skewers on the hottest part of the grill and cook, turning occasionally and moving to a cooler part of the grill as needed to avoid blackening or flare-ups, until browned all over and medium-rare to medium in the middle, 7 to 10 minutes.
Meanwhile, arrange the tomatoes on a large platter. As the skewers are cooked, remove them from the grill to the platter. Drizzle the lamb and tomatoes with the remaining charmoula sauce and serve immediately.