Step 1

Combine yogurt, parsley, tarragon, chives, capers, garlic, lemon zest and 2 tablespoons lemon juice in a medium bowl; whisk until well mixed.

Step 2

Sprinkle avocado evenly with salt and the remaining 2 tablespoons lemon juice.

Step 3

Spread 2 heaping tablespoons of the yogurt mixture on each bread slice. Top each of 2 bread slices with 1/2 cup watercress and cucumber, 4 slices avocado and 1/4 cup alfalfa sprouts. Top with the remaining 2 bread slices, spread-side down. Cut in half and serve immediately.