Peel cucumbers if desired. Cut in half lengthwise and scoop out seeds with a spoon. Dice into 1/2-inch pieces. Place in a colander, sprinkle with a pinch of salt, and let drain for 10 minutes.
In a small bowl, whisk together Greek yogurt, mayonnaise, lemon juice, Dijon mustard, salt, and pepper until smooth. Stir in chopped dill.
In a large bowl, gently fold together crab meat, drained cucumbers, and red onion.
Pour dressing over crab mixture and fold gently until evenly coated. Taste and adjust seasoning.
Serve immediately or refrigerate for 30 minutes to let flavors meld. Garnish with lemon wedges and extra dill if desired.
