01 - Slice cucumbers thinly and finely chop green onions. Place both in a large mixing bowl.
02 - Gently fold crab meat and diced avocado (if using) into the cucumber mixture, taking care not to break up the crab pieces.
03 - In a small bowl, whisk together mayonnaise, sour cream, fresh lemon juice, Dijon mustard, salt, and black pepper until completely smooth and well combined.
04 - Pour the dressing over the salad ingredients and toss gently to coat evenly without mashing the avocado or breaking the crab meat.
05 - Transfer to a serving dish, sprinkle with chopped fresh dill, and arrange lemon wedges on the side.