Green Goddess Chicken Sandwiches

INGREDIENTS

• 4 hamburger buns or sandwich rolls
• 1 cup fresh baby spinach leaves
• 1 avocado, peeled and pitted
• 1 teaspoon kosher salt, divided
• 1/4 teaspoon ground white pepper
• 1/2 cup fresh herbs (I used 2 tablespoons each basil, chives, cilantro and parsley)
• 2 teaspoons fresh lemon juice
• 1 tablespoon honey
• 2 chicken breasts, cut crosswise in half and pounded to 1/2" thickness
• Nonstick cooking spray
• 2 teaspoons white balsamic vinegar
• 7 ounces Greek yogurt
• 1/2 teaspoon ground black pepper
• 1 small clove garlic (or 1/2 of a larger clove)