How to Make It
Place half of the crabmeat gently in the bottom of a large glass bowl or plastic container with a tight-fitting lid, carefully picking out any shell. Sprinkle with half of the salt and pepper. Cover crab with half of the onion slices. Repeat with remaining crab, salt, pepper, and onion slices.
Whisk together oil and vinegar, and pour over layers. Place ice cubes in a liquid measuring cup. Fill with water until volume reaches 1/3 cup; pour ice and water over crab mixture. Cover and chill 2 hours.
When ready to serve, shake bowl gently to mix salad. (If using a leak-proof plastic container, turn upside down and back upright to gently mix salad.) Serve in a shallow bowl with juice. Garnish with cilantro or parsley, if desired.