Soak and clean the zucchini, trim away their ends, and slice them into the thinnest possible rounds.
Set a pasta colander over a bowl or deep dish, put the zucchini slices into it, and sprinkle them liberally with salt. Turn them over two or three times, and let them steep for at least 3 hours, allowing them to shed a substantial amount of liquid. Before cooking them, rinse off the salt with cold water and pat them dry with a kitchen towel.
When the zucchini have steeped 3 hours or more, choose a skillet or sauté pan that can subsequently contain them without piling them up too deep; put in the olive oil, onion, garlic, and pancetta; and turn on the heat to medium high. Cook, stirring a few times, until the onion becomes colored a light gold.
Add the parsley, stir quickly, then put in the zucchini. Turn them over thoroughly for several seconds, then put in the tomatoes and the ground pepper. Turn over all ingredients, turn the heat up to high, and cook, stirring occasionally, until the tomato juices are no longer runny and the fat begins to separate from the sauce, as described in the Note, about 10 to 15 minutes.