Make the lavender tea: Add the dried lavender flower to a glass quart container. Bring half of the water to a boil. Slowly pour about 2 inches of boiling water into the container, then stir with the lavender. Add the remaining boiling water. Cover tightly and steep for 4-10 hours.
Finish the lavender lemonade: Strain out the lavender. Add the liquid to a pitcher along with the remaining water and maple syrup, and squeeze in the lemons. Stir together and refrigerate.
Prep the 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, 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.
Toast the bread.
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 lavender lemonade. Garnish with lavender flowers and serve over ice if desired.
Refrigerate extra lemonade for future use.