Green Goddess Crunch Sandwich

Name: Green Goddess Crunch Sandwich
Ingredients: ¼ cup finely chopped chives; ¼ cup mayonnaise; ¼ cup tarragon; ¼ cup whole-milk Greek yogurt; 1 lemon, halved; 2 tablespoons extra-virgin olive oil, plus more for drizzling; Kosher salt, freshly ground pepper; ½ head of butter or Bibb lettuce (about 2 ounces), large leaves torn; ¼ English hothouse cucumber, thinly sliced; 1 avocado, thinly sliced; 4 slices grainy bread; 8 ounces fresh mozzarella, sliced ¼ inch thick; 2 cups sprouts (such as broccoli sprouts or alfalfa)