Hinjeniero:
I'm trying to avoid the use of resistors to limit the current directly to the led because it's a waste of power. I prefer (if possible) to limit the current trough the MOSFET.
The only way to avoid wasting power when driving large LEDs is to use a switched mode constant current regulator. You can build them yourself around a switching regulator IC, inductor and a few other components, but they can be tricky to design.