Make tzatziki a few hours ahead of time, if you can, so the flavors meld together. If you can't, make it while the eggplant is sitting. Or, you can use store-bought tzatziki if you wish.
Slice eggplant into 1/2 inch circles.
Salt each slice of eggplant on both sides and place in a large bowl so they can "sweat" out the bitter juices. A general sprinkling of salt is ok, it doesn't have to be a lot or too precise. Let eggplant sit for 20 minutes. I try to position the slices in a way that any juices will easily run down and pool at the bottom of the bowl.
While eggplant is sitting, prepare tzatziki. Refrigerate until needed.
Prepare small bowl of flour for dredging.
Once 20 minutes have passed, remove eggplant slices from bowl one by one and dredge in flour on both sides. I don't wash the salt off of the eggplant... I find what is left of the salt seasons them perfectly. If you're concerned about salt intake, you can rinse the slices prior to dredging.
Cover bottom of frying pan or skillet with a layer of olive oil. Heat on medium high/medium heat (you may need to adjust as you're frying).
Once oil is heated, add eggplant and cook on each side for approximately 3-4 minutes or until cooked through and nicely browned. You will likely have to work in batches. You may need to add more oil for each batch as the eggplant tends to soak it up.
Top eggplant with tzatziki and serve immediately.