Incredibly fast and easy, not to mention very tasty! I make mine on a foil-lined tray in my toaster oven, one serving at a time. :) Make as many servings as you like simply by multiplying each ingredient by the number of servings.
Line a shallow pan with foil. Use enough foil so that you can double it back over the top of the dish when it is ready to cook.
Pour olive oil in a fish-size line on the foil. Place fish on top of oil, flipping it over to coat all of the fish in the oil.
Spritz fish with lemon juice (use more or less, to your taste).
Rub garlic across the top of the filet so it is evenly distributed.
Sprinkle feta over the fish evenly. Salt and pepper to taste.
Fold the foil (loosely) over the fish. This isn't critical, but it does help keep the fish moist if you should happen to overcook it.
Bake for 6-7 minutes. Test fish for doneness by flaking with a fork. Flakes should fall apart effortlessly; you shouldn't have to "cut" the fish at all, but rather just separate the flakes.
Some people might prefer to leave the foil off the top if they want the garlic to brown up a bit. I haven't tried this, so I can't say how it would work. You might try removing the foil in the last 2 minutes of cooking or so if you want to give it a shot.