Put the oil, garlic, red pepper flakes and some salt in a large skillet. Heat over a low flame, stirring often, until the garlic begins to sizzle, but before it gets any brown color at all. Stir in the chickpeas. Add the mizuna to the skillet and stir as it wilts. Sprinkle on the sherry wine vinegar, stirring. Transfer to a serving dish and garnish with the nuts.