This is how I got the achievement, and I got to spend my points on whatever i wanted. You just need to get one power fully upgraded.
The absolute easiest way to get this achievement is to load a character from ME2 or 1. Spend all of your points on one power(doesn't matter which one it is). You need 21 points to get to the highest level. Once you level one of the powers up fully, the achievement should unlock right there. If you want to spend your points on other powers, press Y to undo the upgrades. Your points should be returned to you, and you'll have the achievement.
If you DON'T have an imported character, or if you've spent all of your points on different upgrades, you can still get the achievement by going to the Normandy and resetting your points in the Medical Bay. I'd recommend saving here, but its entirely up to you. Go into the Medical Bay and reset your points. As long as you have 21 points, you can fully level up one power. At this point, the achievement should unlock. Either press Y to undo and spend your points on other things, or you can just load the save from earlier.
If you need any help, leave a comment, I'll try to update this and help anyone who needs it.
*Edited for clarity.*