Two for the Price of One Trophy

This can easily be done in the mission where you learn the Devastator ability. The mission is called 'Orion Phase Two' and takes place relatively early in the game, on the first island (Yellow Zone). Right after getting the ability you will need to consume some soldiers to power up your Devastator attack. A cutscene will begin to play and lots of Brawlers will come in (they look like mutated gorillas with devastating claws). Damage two Brawlers until half of their health is gone and hold down + when they are nearby.

You can also get this later in free roam or during other missions. If you have all bio mass upgrades you can also kill the brawlers instantly without damaging them first.