In small bowl, stir together soy sauce, vinegar and sugar. Arrange lettuce leaves on serving platter.
In large nonstick skillet, heat oil over medium-high heat. Add scallions, ginger and garlic; stir-fry 30 seconds. Add red peppers; stir-fry for 1 minute.
Stir the soy sauce mixture, then add to skillet. Add the crab; gently stir-fry for 30 seconds. Spoon over lettuce leaves. Serve warm or at room temperature.