In a bowl, combine yogurt, cucumbers, garlic and juice; set aside. In another bowl, mix beef, zucchini, feta, onion, marjoram, salt and pepper. Form beef mixture into four 3/4-inch-thick patties. Coat a grill pan or grill rack with cooking spray. Grill patties over medium-high heat, flipping once, about 5 minutes each side, until internal temperature reaches 160°F Divide roasted peppers evenly among bottom roll halves; top with 1 burger, 1/4 yogurt sauce and lettuce and cucumber, if desired. Top each with other half of roll.