There are two ways to go about this achievement. There is the easy way, or there's the somewhat annoying way.
The easy way can only be done at the very beginning of the game. After customizing Mike, you will be given the option by Westridge to either go and finish some training exercises, or meet back with him. During this time, you'll want to go through the Gadget Training with Sean Darcy, which you'll start by going to a nearby locker and grabbing some gadgets. You will be told by him to lob grenades at some targets, but don't do that right away. Instead, plant these grenades by either looking all the way down at the ground, or near a wall while holding . If close enough, a red silhouette will appear, and once you release , your grenade will be planted. Keep planting all your grenades in the same area until you get to your last one, which you'll want to throw into the group. If done correctly, all the grenades will blow up. From there, just go back to the locker for more grenades, and repeat until you get the achievement.
If you're already past this point in the game, you'll have to follow the somewhat annoying way. After you finish a mission, always stock up on more Remote Mines via the Clearinghouse. They can be thrown, but will not detonate until you hit again. Just use them like you would a normal grenade against enemies, and eventually the achievement will unlock.