Bring a small pot of water to a boil and salt it. Poach peas in water until bright green, about 30 seconds, and remove with a slotted spoon; drain and cool for a few minutes. If you would like a milder flavor, poach onions for 15 seconds, and remove with a slotted spoon; drain and cool for a few minutes.
In a bowl, combine peas, onion, bell pepper, crab, olive oil, lemon juice and some salt and pepper; taste and adjust seasoning as necessary. To serve, spoon into lettuce cups or on top of endive leaves; garnish and serve.