Combine shredded chicken with chicken stock in a sauce pot. Simmer until liquid is reduced by 1/2.

Add sherry, mustard, onions, peppers, and garlic. Simmer until liquid reduces by 1/2 or until chicken is thoroughly heated. Alternatively, after removing chicken and veggies add a cornstarch slurry to thicken liquid to use as a sauce. (1 T cornstarch whisked into 1/4 C cold water)

Assemble sandwich with mayonnaise on bottom, chicken and veggies, avocado, and horseradish. Toast in oven or panini press.

Variations; Vinegar, apple juice, lime, lemon, tomato, arugula, lettuce, spinach, tamarind, soy, worchestershire, shallots, habanero, celery, bacon, basil, parsely, cilantro, scallions, jalapeño, gruyere, parmesean, roasted bell peppers, sourdough, swiss, aioli, cayenne, caramelized onions, pickled veggies, crushed pepper flakes, corn, zucchini,