Remove the roots and damaged leaves from the spinach, then wash it thoroughly, changing the water several times. Put it in a saucepan while still dripping wet, put the lid on and cook for a few minutes; stir from time to time until the leaves soften and diminish in volume. Strain off the water when the spinach it's still "al dente" (the leaves mustn't fall apart), wait 5 minutes for it to cool a bit an then squeeze it well, forming small balls. Chop the spinach. Cut the pancetta into strips and cook it in a heavy-bottomed frying pan with the oil. Add the spinach and toss it in the pan with the pancetta for 5-6 minutes. Season with salt and freshly ground pepper and serve while hot.
A tasty side dish that's quick to prepare - you can also make it with spinach cooked in advance!