Combine yogurt and 1/4 cup tapenade in small bowl. Cover and refrigerate until ready to use.
Combine Ground Beef and remaining 1/4 cup tapenade in large bowl, mixing lightly but thoroughly. Lightly shape into four 1/2-inch thick patties.
Heat grill pan over medium heat until hot. Place patties in pan; cook 10 to 12 minutes until instant-read thermometer inserted horizontally into center registers 160°F, turning occasionally. Season with pepper, as desired. Remove; keep warm.
Place 1 tablespoon cheese on bottom of each bun; top evenly with spinach leaves, onion, burger and zucchini. Spread 2 tablespoons yogurt mixture on cut side of each bun top. Close sandwiches.
Test Kitchen Tips: Cooking times are for fresh or thoroughly thawed Ground Beef. Color is not a reliable indicator of Ground Beef doneness.
Nutrition information per serving: 406 calories; 19 g fat (6 g saturated fat; 4 g monounsaturated fat); 74 mg cholesterol; 655 mg sodium; 30 g carbohydrate; 4.8 g fiber; 30 g protein; 7.3 mg niacin; 0.6 mg vitamin B6; 2.3 mcg vitamin B12; 5.3 mg iron; 34.0 mcg selenium; 6.4 mg zinc.
This recipe is an excellent source of fiber, protein, niacin, vitamin B6, vitamin B12, iron, selenium and zinc.