In a medium skillet, cook the chopped pancetta over moderately high heat, stirring occasionally, until it is crisp, about 8 minutes. Using a slotted spoon, transfer the pancetta to a plate. Pour off all but 1 tablespoon of the fat in the skillet. Add the sliced onion, cover and cook over moderate heat until it is softened, about 5 minutes. Add 2 tablespoons of water to the skillet and cook, stirring occasionally, until the onion is lightly browned, about 5 minutes longer. Stir in the cumin and season the onion with salt and pepper.