If you don't have any logicc level MOSFET around (which would be BY FAR the best choice), you might be able to use a diode-based level translator such as the one attached. You should size the resistors so that the "idle" voltage on the MCU GPIO pin is lower than 3.3V, in order to be on the safe side. When the GPIO pin outputs 0V, the Vgs on the IRF520 is two diode drops (1.2 to 1.4V) which is lower than the specified minimum threshold voltage, so the transistor should stay OFF (at least as long as it stays cool, as the threshold drops with temperature), and when the GPIO outputs 3.3V the Vgs should be around 4.5 to 4.7 V, which is enough to turn it on, although just barely. As long as the current through the LED is low, you might be able to make it work.
The switching time of the FET will be quite slow, so don't push the PWM frequency.
Furthermore, if you sourced the FETs from eBay or Aliexpress the threshold voltage might be different and this circuit might not work or might need adjustments.