Heat the olive oil in a 10-inch ovenproof sauté pan over medium heat. Add the pancetta and sauté for 5 minutes until it begins to brown. Rinse the leeks well, spin-dry in a salad spinner, add to the pan, and sauté for another 5 minutes, until tender. Add the zucchini and thyme and toss. Cook for 5 to 6 minutes, stirring occasionally, until the zucchini is tender.