Mix garlic, cilantro, parsley, onion and salt in medium bowl.
Mash 1 ½ cups beans in medium bowl, reserving ¼ cup whole bean for later use.
Add bread crumbs, hummus, chili powder and whole black beans; mix well.
Shape mixture into 4 (3-inch diameter) patties about ½-inch thick.
Cover and refrigerate 30-40 minutes.
Attach bottom grill plate to Grill & Broil.
Lightly oil plate and preheat on HIGH Broil at 400°F.
Place 2 patties on Grill & Broil for 6 to 8 minutes, turning over halfway through cooking.
Repeat for remaining patties.
Fill buns with patties topped with tzatziki sauce.