Greek Feta Beef Burger

Name: Greek Feta Beef Burger
Ingredients: 6 oz nonfat plain Greek yogurt; 4 ounces hothouse cucumbers (unpeeled), coarsely grated (about½ cup); ½ clove garlic, crushed to a paste; 1 teaspoon fresh lemon juice; 1 lb lean ground beef (93 percent or 95 percent lean); 4 ounces zucchini, finely diced (about 1 cup); ½ cup crumbled reduced-fat feta; ⅓ cup finely diced red onion; ½ teaspoons dried marjoram; ½ teaspoon salt; ¼ teaspoon freshly ground black pepper; Vegetable oil cooking spray; 1 jar (7 oz) roasted red peppers, drained; 4 sourdough rolls, split; Shredded romaine (optional); Sliced cucumber (optional)