1) Salt the zucchini
Spread zucchini rounds on a paper-towel-lined sheet pan. Sprinkle with 1 tsp of the salt. Let sit for 10 minutes (not much longer, or the slices can go limp), then pat very dry. Moisture is the enemy of crunch.
2) Mix the dip
In a small bowl, stir together mayo, sour cream, lemon juice, lemon zest, garlic, herbs, and a pinch of salt and pepper. Refrigerate while you fry.
3) Set up the dredge
In a shallow bowl, combine flour, cornmeal, Parmesan, garlic powder, onion powder, paprika, pepper, and the remaining 1/2 tsp salt.
In a second bowl, whisk eggs with milk.
4) Heat the oil
Add oil to a large skillet to reach about 3/4 to 1 inch depth. Heat to 350°F over medium to medium-high heat. If you do not have a thermometer, drop in a pinch of coating. It should sizzle and bubble right away.
5) Coat the zucchini
Working a few at a time, dip zucchini into the egg, let excess drip off, then press into the seasoned flour mixture. If any pieces look damp, give them a quick blot before coating so it sticks like it means it. Set on a plate while you finish a batch.
6) Fry in batches
Fry zucchini rounds in a single layer for 2 to 3 minutes per side, until deeply golden with crisp edges. Do not crowd the pan, or the oil temp will drop and you will get soggy zucchini.
Parmesan can brown quickly, so if the coating is getting dark before the zucchini is tender, nudge the heat down a bit to keep things in the golden zone.
Transfer to a wire rack set over a sheet pan. Sprinkle with a tiny pinch of salt while hot.
7) Serve bright
Serve immediately with lemon wedges and the lemon herb dip. If you want extra swagger, dust with a little more Parmesan right before serving.