INGREDIENTS

• 3 tablespoons mayonnaise
• 1 tablespoon nonfat plain Greek yogurt
• 1 teaspoon grated lemon zest plus 1 tablespoon juice
• Salt and pepper
• 1 can (5 ounces) solid light tuna packed in water, drained and flaked
• 1 stalk celery, halved lengthwise and thinly sliced
• 1/2 Granny Smith apple peeled and grated
• Whole-wheat bread, red onion, cucumber and alfalfa sprouts, for serving