Step 1

Whisk sour cream, mayonnaise, garlic, lemon zest, lemon juice, salt, and pepper in a medium bowl to combine.

Step 2

Do Ahead: Dressing can be made 1 day ahead. Cover and chill.

Step 3

Trim root end of lettuce; discard any wilted outer leaves. Cut into quarters lengthwise, then cut each quarter crosswise into 3" pieces. Without separating wedges into leaves, transfer to a large platter. Tuck avocado pieces among lettuce and drizzle lemon juice over; season with salt.

Step 4

Spoon half of dressing over salad and top with chives; season with pepper. Serve with remaining dressing alongside.