Before you start cooking, it's important to get yourself a very large pan, or use a high-sided roasting pan so you can give the pasta a good toss.
Put a large pan of salted water on to boil. Halve and then quarter any larger zucchini lengthwise. Cut out and discard any fluffy middle bits, and slice the zucchini at an angle into pieces roughly the same size and shape as the penne. Smaller zucchini can simply be sliced finely. Your water will now be boiling, so add the penne to the pan and cook according to the package instructions.
To make your creamy carbonara sauce, put the egg yolks into a bowl, add the cream and half the Parmesan, and mix together with a fork. Season lightly with salt and pepper and set aside.
Heat a very large frying pan (a 14-inch is a good start - every house should have one!), add a good splash of olive oil and fry the pancetta or bacon until dark brown and crisp. Add the zucchini slices and 2 big pinches of black pepper, not just to season but to give it a bit of a kick. Sprinkle in the thyme leaves, give everything a stir, so the zucchini is coated with all the lovely bacon-flavored oil, and fry until they start to turn lightly golden and have softened slightly.
It's very important to get this next bit right or your carbonara could end up ruined. You need to work quickly. When the pasta is cooked, drain it, reserving a little of the cooking water. Immediately, toss the pasta in the pan with the zucchini, bacon and lovely flavors, then remove from the heat and add a ladleful of the reserved cooking water and your creamy sauce. Stir together quickly. (No more cooking now, otherwise you'll scramble the eggs.)
Get everyone around the table, ready to eat straightaway. While you're tossing the pasta and sauce, sprinkle in the rest of the Parmesan and a little more of the cooking water if needed, to give you a silky and shiny sauce. Taste quickly for seasoning. If you've managed to get any zucchini flowers, tear them over the top, then serve and eat immediately, as the sauce can become thick and stodgy if left too long.