1/2 cup (2 ounces) crumbled feta cheese
2 tablespoons light mayonnaise
2 tablespoons plain fat-free yogurt
1/4 teaspoon coarsely ground black pepper
1 garlic clove, minced
5 (1/2-inch-thick) slices red onion
Cooking spray
1 pound lean ground round
2/3 cup fresh breadcrumbs
1/3 cup chopped bottled roasted red bell peppers
1/4 cup chopped fresh parsley
1 teaspoon dried oregano
1/4 teaspoon salt
1/4 teaspoon coarsely ground black pepper
1 (10-ounce) package frozen chopped spinach, thawed, drained, and squeezed dry
1 large egg, lightly beaten
2 garlic cloves, crushed
5 (1 1/2-ounce) sourdough sandwich buns