How to Make It
Light a grill. In a large bowl, combine the lamb with half of the garlic, the 1/2 teaspoon of oregano and the mint, cinnamon, salt and pepper. Mix gently and pat into 6 burgers. Let stand for 15 minutes.
Meanwhile, in a food processor, combine the olives with the remaining minced garlic and process until coarsely chopped. Add the 1/4 cup of olive oil and process to a paste. Scrape the tapenade into a bowl and stir in the parsley.
Brush the burgers with oil and grill them over a hot fire until medium-rare, 4 minutes per side. Carefully put the feta slices on the grill and grill just until hot, about 10 seconds per side. Sprinkle the feta with oregano and set each slice on a burger.
Spread the tapenade on the rolls. Top with the burgers and the tomato slices. Close the sandwiches and serve.