Burning Bridges is an ideal mission to get this achievement, and it's not as hard as it sounds. You'll get ample reinforcements all of the Spec Ops class, who are all equipped with C4.
Start the mission by switching to the closest sniper. Use him to take out the helicopter with his laser designator, and then snipe the guards in the towers in front of the bridge. Now switch back to Special Ops for the rest of the mission.
The enemies in this level will run directly towards you from one direction, which gives you great opportunities to use C4. Just stand behind cover and near corners, and lob C4 out in the direction the enemies are coming from. Great choke points for this are the machine gun nest next to debris facing the bridge, standing to the right of the bridge entrance, and behind any of the downed vehicles along the bridge.
Remember, while you'll unlock the achievement immediately, make sure you DON'T QUIT once it unlocks; either finish the mission or just fail...if you quit, it won't save the medal towards your campaign progression!