Lay the fillets out on a cutting board and remove any pin bones. This can be done by pulling individual bones or cutting out the strip of meat around them.
Place 2 Tbs of butter in a large frying pan (I prefer cast-iron) over Med-High heat. Let the butter and pan heat up as you prep the fish.
If rockfish fillets are more than 1 inch thick, fillet them in half.
Cut fillets long-wise into 1 to 2 inch strips following any striations, then cut cross-wise creating chunks of fish no larger than 2x2 inch squares.
Lay chunks of fish out on cutting board and generously sprinkle the top sides with lemon pepper and cumin.
Using tongs, lay 1 chunk of fish upside down in hot pan to check that butter and pan are ready. If the butter sizzles, then it is ready for the rest of the fish.
Lay the remaining fish chunks upside down in the hot pan.
Generously sprinkle the top sides with lemon pepper and cumin.
As the fish cooks, it will change color & texture. The thinner pieces may start to curl, and the cooked meat will turn opaque. Turn the thin pieces over first, letting the thicker pieces continue to cook.
If the bottom of the pan looks dry or fish is difficult to flip, you can add butter to the pan, 1 Tbs at a time.
Turn the thicker pieces over when you can tell that they are cooked ½ way through their thickness.
Remove individual fish chunks from pan when they become flakey. Check them by pressing on them with tongs and let them crumble into pan.
Do not overcook fish, or it will become dry and tough.
After fish is done and while pan is still hot, carefully pour a thin layer of water into pan to steam clean. As it cools, you should be able to scrape off any cooked-on remnants.