You'll see a few groups of chickens in cages throughout this level. After you pass through the market, you'll come to a spot leading to an alley with two different groups of 5-6 chicken cages and another group of 4-5 - that's the spot you want to focus on for this trophy.
Toss a grenade at one of the larger groups and then open fire on the other one and you should get this no problem. If you want to, turn around and fire into the smaller group as well for good measure, but you shouldn't need it. Remember - if you run out of bullets at any point, switching weapons is faster than reloading.