In a small bowl, combine the chicken and cornstarch. Season lightly with salt and pepper and set aside.
In a medium bowl, whisk together the rice wine vinegar, soy sauce, peanut and sesame oils, and the sherry wine vinegar. Add the spinach, celery, carrot, and onion, and toss and season with salt and pepper, to taste. Using 2 large or 3 small radicchio leaves for each serving, form 4 cups and arrange on a large serving platter. Divide the salad among the cups and set aside.
In a 10-inch skillet, heat the peanut oil over high heat until smoking. Form the chicken into 1 large patty and carefully set in the pan. Let brown on 1 side, then stir in the garlic, ginger, green onions, and chili pepper flakes, breaking up the patty, and continue to stir until the chicken is browned. Pour in the rice wine vinegar, plum wine, soy sauce, and stock, and reduce until most of the liquid has evaporated. Correct seasoning, to taste.
Divide the chicken mixture and spoon equal amounts into the radicchio cups. Sprinkle with the chopped mint or cilantro.