Step 1

Place basil, chives, mayonnaise, yogurt, and 2 Tbsp. oil in a blender. Finely grate in zest from a lemon half, then squeeze in its juice. Purée until smooth; season dressing with salt and pepper.

Step 2

Place cucumber in a small bowl; squeeze in juice from remaining lemon half. Drizzle with oil, season with salt and pepper, and toss to coat.

Step 3

Spread one side of each slice of bread with dressing. Divide avocado between 2 slices of bread; season with salt and pepper. Top with cucumber, mozzarella, and sprouts and close up sandwiches.