Place a layer of parchment paper on the bottom of your oiled pan, spray more oil, and place the fish filet on top. The fish will cook perfectly and there will be nothing to scrub.
Most parchment paper has a temperature limit of around 425°F, which isn't hard to exceed. If you do, the parchment paper will turn brown or black, which can end up on the fish.
Also keep in mind that parchment paper is flammable, especially if you use a gas stove. While the parchment paper trick does work, it's best to use a nonstick pan, if you have one.