First, make the filling. Add the pork, garlic, scallions, soy sauce, sesame oil and ground pepper into a a large mixing bowl. Use a pair of chopsticks (or your hands) to mix the filling together until combined. Set aside to let the flavours come together.
Next, prepare the zucchini. Slice the zucchini into 1-inch thick slices. Use a melon-baller to scoop out the seeds in the center of the zucchini rounds. Make sure to not scoop through to the bottom of the zucchini, leaving about 1cm at the bottom to hold the meat and juices in the zucchini as it cooks. Continue the process until all the zucchini rounds have been hollowed out.
To stuff the zucchini, take 2-3 tablespoons of the pork filling and scoop it into the center of each zucchini rounds. Pack the filling into the zucchini tightly so that there are no air pockets. Repeat the process until all the zucchini rounds are stuffed.
Place the stuffed zucchini in an even layer in a large frying pan or pot. Add the chicken broth, cover with a lid, and then bring the contents to a boil. Once boiling, reduce the heat to medium and let the stuffed zucchini simmer for 15 minutes, or until the meat is fully cooked and the zucchini is tender.
In the meantime, mix the cornstarch and water until combined and there are no lumps. Once the stuffed zucchini is cooked, turn the heat to high, add the cornstarch mixture, and mix to combine.
Once the sauce has thickened, remove it from the heat and serve!