Prep sandwich ingredients per the instructions above.
Make green goddess dressing: Place chives, mayonnaise, tarragon, and yogurt in a blender along with zest and juice of the lemon, oil, salt, and pepper to taste. Purée until smooth.
Squeeze juice from the remaining lemon half over lettuce and cucumbers in a medium bowl. Drizzle with oil; season with salt and pepper. Toss to coat.
Spread the dressing on one side of each slice of bread.
Layer the bottom slice of bread with lettuce, cucumbers, mozzarella, sprouts, and avocado. Season with salt and pepper.
Serve: Cut the sandwich in half. Enjoy with chips, pickle, and kombucha.