6 ounces nonfat plain Greek yogurt
4 ounces hothouse cucumbers (unpeeled), coarsely grated (about 1/2 cup)
1/2 clove garlic, crushed to a paste
1 teaspoon fresh lemon juice
1 pound lean ground beef (93 percent or 95 percent lean)
4 ounces zucchini, finely diced (about 1 cup)
1/2 cup crumbled reduced-fat feta
1/3 cup finely diced red onion
1/2 teaspoon dried marjoram
1/2 teaspoon salt
1/4 teaspoon freshly ground black pepper
Vegetable oil cooking spray
1 jar (7 ounces) roasted red peppers, drained
4 sourdough rolls, split
Shredded romaine (optional)
Sliced cucumber (optional)