with the MOE hand guard, if it's the pre-M-LOK style, you have 4 mounting options (or so). If you want to go with the pistol light on there, you can just use a rail section. If you want to use a regular flashlight, you can get the magpul light mount (cheap, effective, but clunky), the IWC MOE light mount (light weight, low profile, but a bit more money), or the Arson Machine MOE light mount (a bit more versatile than the IWC, but still costs more than the Magpul mount).
I will say, having messed around with my TRL-1 on my MOE Carbine, I didn't really like it on there. Actuating the switch is kind of awkward for me. I didn't really like it. I just run a SureFire G2X Tactical on it with a MOE VFG on the bottom as a hand stop and it is just about perfect for me. Very quick and intuitive to use.