In a medium saute pan, render the guanciale or pancetta over low heat until it becomes crispy, stirring regularly, about 10 minutes. Add the pistachios and stir for about two minutes more.
Add the dandelion greens, flowers and onions, and remove them from the heat.
Toss the contents of the pan in the pork fat until the greens and onions wilt slightly, then transfer to a large bowl or platter and serve warm. Balance with the juice of the lemon, to taste. Serves 4 as a side dish.