For the Tzatziki:
Combine all ingredients in a bowl, and mix well using a rubber spatula. Chill before serving, garnishing with more olive oil on top, if desired.
For the zucchini and eggplant chips:
Heat oil in a deep-sided pan to 375 degrees F.
Dredge the eggplant and zucchini rounds in the flour, coating well. Shake off excess flour and set aside. Taking a few rounds at a time, dip in cold water, and immediately put into hot oil (oil may splatter). Cook until golden brown and crispy. Remove from oil using slotted spoon, and put into stainless steel bowl. While tossing continuously in the bowl, sprinkle with salt and oregano, to taste. Serve with the Tzatziki.