Place crabmeat in a medium bowl. Drizzle with lemon juice to moisten. Transfer to the refrigerator for 30 minutes.
Drain off any accumulated juice, pressing crabmeat slightly. Gently stir in mayonnaise, pimiento, scallion, and pickles. Season with salt and pepper.
Evenly divide crabmeat mixture between avocado halves. Top each with a dollop of dressing, and garnish with capers.