Place the chicken breasts in cold water in a 4-quart pot. The water should cover the chicken breasts. Slowly bring the water to a boil and poach the chicken breasts at a bare simmer for 5 minutes. Cool the chicken in water for 15 minutes. Remove from the water. Tear off the skin and separate the meat from the bones. Shred the chicken into pieces about 2 inches by 1 inch.

Combine the peanut butter, sesame paste, mayonnaise, soy sauce, vinegar, and garlic in a blender or food processor. Season with 1 teaspoon salt and ¼ teaspoon pepper. Taste and adjust the seasoning.

Combine the dressing with the chicken and serve immediately, or marinate for 2 hours.*

To serve, place the chicken salad on lettuce leaves and garnish with sliced scallions.