Fish Katsu

In addition to the above ingredients, you'll need a kitchen cloth or paper towels, a shallow bowl for beaten eggs, 2 plates for prep, 1 heat resistant plate for finished fried fish (with a wire grate as well if available), pan for frying, 2 heat resistant spatulas (one kind of wide to get under and support a fillet), canola or equiv oil for frying.

If the fillets are thick or particularly wide (more than 3"?) you may want to cut them in half length-wise to guarantee the interior gets cooked, and make the prep/frying easier.

The theory here is that the flour absorbs moisture given off by the fish during frying, the egg is a binder between the flour layer and panko crumb outside.

1. Let the fish warm to room temp, or close. Then dry the fish with a kitchen cloth or paper towels. Press don't wipe, to avoid damaging the flesh side. If the fish was thawed, it will express more moisture due to freezing damage, so put some pressure into the drying to get more moisture out, maybe moving the fish around on the cloth to use different dry areas. BTW, there's a Japanese technique called Shioyaki where you salt the surface to draw out moisture, letting it sit for some time and then quickly rinsing the salt off and drying. (But this recipe isn't that ;-)
2. Put a thin layer of flour on a plate, sprinkle with salt and pepper to taste, and then one at a time, dip/press each fillet into the flour, flipping to get both sides. Inspect to find and cover all fillet surfaces with flour. You can do this in a bowl as well or whatever seems easiest to you. Let fillets rest while proceeding to ...
3. Break the egg(s) into a shallow bowl that you can lay a fillet in, or mostly so. Add some salt (I tend to use fish sauce). Beat with a fork or whisk. Depending on how much fish you have you might want 2 eggs.
4. Cover a plate with panko so the plate surface doesn't show. Keep the panko bag handy.
5. Put a ¼" or so layer of oil into the frying pan and heat it to medium high. If you can't fry all the fish in a single batch, turn on the oven as well to, say, 250° F to keep the first batch warm.
6. On a counter near the frying pan, arrange the plates - panko plate nearest the pan, then the egg bowl near that.
7. When the oil is hot enough (a pinch/sprinkle of panko into it sizzles), give the fish another light dip of flour to cover any damp spots. Shake off excess flour. I tend to hold the fillets by one end when doing this whole process, like holding a fish by the tail.
8. Taking a fillet by the 'tail' dip it into the egg, flipping to get both sides and the end you're holding. Let excess eggs drip off back into the bowl for a second and then lay the fillet onto the panko plate (keeping the same hold on the fish). Press lightly and then lift and flip and repeat on the other side. Your fillet holding fingers will get covered in egg and panko, live with it (I usually rinse it off between batches). You may want to use your other hand to pinch and sprinkle more panko on a fillet to guarantee coverage. N.B. make sure you have enough panko on the plate for a fillet before doing that fillet ;-). Lay the fillet into the frying pan. Add enough fillets to the pan to fit, but they shouldn't touch each other. You'll need some space to turn them.
9. After a few minutes, but longer than you might think, use 2 spatulas to check done-ness by color - you want a medium toasty brown. I do this by parking one spatula on one edge and use the other spatula to get under the fish on the other side to lift. When a fillet side is done, use the same spatula technique to turn the fillet over and then flip. The fillets are delicate so be careful, also, hot oil and all that ...
10. After both sides of a fillet is done, lift it out with a spatula, onto a plate with paper towels or better, a wire grate of some sort to hold the fillets off of the plate surface (they will continue to emit moisture that will condense under them if in contact with the plate, getting them prematurely soggy). If doing more than will fit in the pan at one time, put the above (ceramic or otherwise heat resistant) plate of done fillets in the warm oven while others fry. This way they can all be served hot with a crispy outside.