In a blender or food processor, combine chives, mayonnaise, tarragon, yogurt, lemon zest, lemon juice, and olive oil. Blend until smooth and creamy, about 30 seconds.

In a medium bowl, add washed lettuce leaves and diced cucumbers. Drizzle with a splash of lemon juice, a bit of olive oil, and season with salt and pepper. Toss until well coated, about 1-2 minutes.

Slice a ripe avocado in half, remove the pit, and mash the flesh in a bowl. Spread it evenly over two slices of bread, and season with salt and pepper.

On one slice of bread, layer the lettuce and cucumber mixture generously over the mashed avocado. Add slices of mozzarella and sprinkle sprouts on top.

Spread the green goddess dressing onto the second slice of bread, then place it atop the sandwich, dressing side down. Press gently to compact and meld flavors.

Using a sharp knife, slice the sandwich in half diagonally and serve with vegetable chips or a light salad.