Defeat Tatsuo without restocking your ammunition from the UAVs, on normal or hard difficulty
This fight is at the end of Chapter 4. The easiest way to go about this fight is utilizing your overlay to shoot at Tatsuo and avoiding him otherwise whenever you need to let your overlay recharge. As the achievement says, do not restock your ammunition (aka do not breach) the floating UAVs during the fight. If you run out of ammo, just pick up any of the guns dropped by enemies before and during the boss fight. If you are careful and use timed shots and shoot only during overlay, though, you shouldn't have to even change guns.
I'd recommend you have the 'Beast of Burden' skill unlocked... it allows you to carry twice the amount of ammo then you normally could. Makes it simple. If you don't want to have that... start picking ammo off the ground on the run. :) There should be enough.