Sol's Disapparate works like this: It's about a 6 second cycle. After using it, she will "burn away" over 3 seconds, becoming faster and immune to slows. During the next 3 seconds, she will leave a trail of fire behind her. At the end of the cycle, the trail she has left behind will explode, stunning any enemies standing on it.
You'll likely get this achievement before you master Sol. However, if you're not familiar with her and you just want to get the achievement done quickly, try this tactic...
Fire off your Disapparate a few seconds before you dive into groups of 2/3 enemies. As they try to gank you - and they probably will - just weave between them, trying to make a small "field/area of fire" instead of just a line. It may help to move backwards/strafe while doing this, allowing you to see the trail you're leaving and where the enemies are in relation.
Easily achieved within the first few minutes of an Arena match.