1
Liberally coat a large skillet with oil spray, and preheat it over medium-high heat.
2
Add the carrots, celery, bell pepper, water chestnuts, scallions, ginger, and garlic. Sauté, stirring occasionally, until the vegetables soften slightly, about 5 minutes, adding a tablespoon of water at a time as necessary to prevent scorching.
3
Reapply oil spray if necessary, and add the ground chicken to the skillet. Cook until the chicken is no longer pink, breaking the meat into a fine crumble with a wooden spoon as it cooks. Season with the black pepper.
4
Add the plum sauce, soy sauce, vinegar, and chili paste and stir to coat. Reduce the heat to low and simmer until heated through.
5
Remove the skillet from the heat, and stir in the cashews and cilantro. Allow the mixture to cool slightly, about 5 minutes.
6
Clean the lettuce and break off 12 individual leaves (trim away the stem end of the leaves if they are tough). Fill each lettuce cup with roughly ½ cup of the chicken mixture. Garnish with additional cilantro if desired.