Finely chop the chicken in a food processor, or use a chefs knife to finely mince. In a small skillet over medium high heat, heat oil and sauté chicken for 5 to 8 minutes, or until opaque throughout.
In a medium bowl, combine the cooked chicken and remaining fillin ingredients. Cover and refrigerate for at least 30 minutes or overnight. Taste and adjust the seasoning with lime juice, fish sauce, and cayenne.
To serve, spoon 1 heaping tablespoon of filling into each lettuce leaf and serve.