Cut zucchini into large chunks. In a food processor with the blade attachment, process 1 pound (2/3 of the total) of zucchini for 10 seconds, or until finely chopped. Pulse 1-2 times more to get any large chunks.
Transfer the chopped zucchini to a large bowl. Switch the processor to the shredding attachment and shred the remaining 1/2 pound of zucchini; then transfer it to the bowl with the rest.
Salt the zucchini and toss to combine. Set aside for 10-15 minutes.
Then scoop the zucchini into a clean kitchen towel and squeeze it until most of the liquid has been removed.
Rinse out the large bowl you were using and put the squeezed zucchini in the bowl. Add the parsley and scallions and stir.
Then add the rice flour, baking powder, and eggs. Mix well. Gently stir in the crumbled feta.
Let the fritter batter rest for a few minutes while you heat up the skillet.
Add enough oil to a 12 inch skillet to coat the bottom. Heat the skillet on medium until the oil is shimmering and hot.
Set out a platter or baking tray lined with paper towels.
Working in batches, scoop out portions of batter which measure about 2-3 tablespoons. Flatten each scoop into a patty and lay it into the hot oil. Don't overcrowd the skillet.
Fry 2 minutes to a side, until the patties are golden brown and crispy, adding more oil as necessary. Transfer the cooked fritters to a the prepared tray.
To make the tzatziki sauce: Add all ingredients to a medium bowl. Stir to combine. Taste and adjust the seasonings if necessary.