Nothing fancy, this; but that's okay: dinner was done and on in the table in exactly 15 minutes (disclaimer: I had to go to the supermarket, wash dishes, clean the cast-iron pan, etc—you didn't think it would really be 15 minutes, did you?). Take your tilapia fillets, add salt and pepper and squeeze out a lemon onto both sides. Meanwhile, get your well-seasoned cast iron skillet to medium-high temperature and coat the bottom with olive oil. Lay your fillets down in the pan, away from you to avoid splattering yourself with hot oil. Try to avoid flipping or moving it more than is strictly necessary as it will fall apart when it gets close to done; I'd recommend flipping with a spatula rather than tongs for the same reason.
Cook for three minutes per side, which should give it a golden-brown surface and just-barely-done center; the thinner parts of the fillet will get crispy, but that's part of the appeal. Serve with salad and rice or whatever you want. Some brown crispy bits will be left in the pan which just cry out for deglazing and making into a pan sauce, but I haven't experimented with that just yet.
I promise not to let this site become a recipe blog. I post things like this really more for my own reference (the three minutes per side number is something I tend to forget).