Peel the cucumber. Slice in half lengthwise, and scrape out the seeds with a teaspoon. Grate the cucumber using the large holes on a box grater, or the grating blade in a food processor. Toss the cucumber with the fennel and ½ teaspoon kosher salt and place in a strainer over a bowl, or in the sink.
Season the fish with salt and pepper. Place the egg and panko into two separate shallow bowls. Stir the parsley into the panko.
Heat the oil in a large skillet over medium high heat. Dunk each fillet in the egg, so that is it well coated, then dredge each filet in the panko mixture. Place the coated fillets in the hot oil and sauté the fish for about 3 to 4 minutes on each side, until cooked through and golden brown. Transfer the fish to a paper towel lined plate.
Use your hands to squeeze the cucumber mixture to press out any extra liquid, then place in a medium bowl. Add the mint, oregano, lemon juice, garlic and yogurt. Stir well, and add pepper and any additional salt as needed (remember the cucumbers and fennel were salted at the beginning).
Serve the fish hot, with a spoonful of tzatziki sauce on the side.
Notes
Different cultures have their own versions of cucumber yogurt sauce, and if you like tzatziki, it’s worth digging in deeper. And if you like tzatziki as much as I do, make extra to serve up with pita chips the next day, or perhaps dollop on a piece of grilled chicken or a chop.