There's a pretty good spot for picking up this Achievement early in the game on Cato Neimoidia. After you've gone through a few areas where you've got the big honeycomb-style globes.
There will be a section where you've got a rather long skyway connecting a smaller round platform to a much larger round platform. There will be an AT-MP that will come out from both the left and the right of the main chamber. You can stay well back from them and lob the missiles back at them as needed.
You may need to whittle away at the stormtroopers that will cluster at the other end of the bridge, but once they're gone, it's just you and the AT-MPs. Also, I found that if the AT-MPs were just standing around, simply walk onto the bridge, and that will trigger them to try to attack you. Cross the line, wait a second, then hop back a bit.