Take the fish out of the fridge, salt both sides, and let it sit for 20 minutes to reach room temperature.
Heat a large steel or cast-iron pan over high heat, then add oil and swirl it around.
Pat the fish dry with paper towels; if it has skin, scrape it dry with a butter knife to remove any slime.
Place the fish, skin side down, in the pan and jiggle it immediately to prevent sticking. Press down gently with a spatula or bacon press for 30–60 seconds.
Baste the exposed side with hot oil by tilting the pan, cooking until the fish turns opaque, about 30 seconds to 1 minute.
Lower the heat to medium-high and let the fish cook undisturbed for 4–6 minutes until it releases naturally from the pan.
Flip thick fillets for another 3–5 minutes of cooking, or remove thinner fillets directly. Serve skin side up and season with pepper.