Tie Fighter's appear only on some of the Death Star levels. You need to defeat a Tie Fighter, which causes it to explode and its two wings to pop off. To get the achievement, you need to have one of the broken-off wings hit a Stormtrooper. This is obtainable on many levels and you will likely get it without trying. An easy level to do this on is 2-37. Shoot your first bird down the middle. Time your shot and use the lasers to blast the body of one of the circular moving Tie Fighters inside the largest gravitational field. Within a few tries, you should be able to get the one of the wings to hit one of the Stormtroopers.