Specific code would help - and EVAP leaks can be caused by something as simple as your gas cap not being tightened enough, or cross-threaded. Old gas caps can have the seal degrade. If you put a non-OEM cap on, and it's not a good match - that could cause this.
A quick search for "Evaporator Leak" turned this up.
- Your gas cap is either loose or incorrectly attached
- Your gas cap does not meet vehicle manufacturer standards
- You have a tiny leak, crack or hole in a fuel vapor hose or tube
- You have a different type of leak somewhere in the EVAP system
- You have a faulty vent or purge valve
- You have a bad vent seal
- You have an unreliable leak detection pump in the EVAP system
Without more info - it's hard to diagnose or tell you where to start - but I'd start with the gas cap.
Note: It will take two or three days of driving (or about 50-60 miles) to clear the code if it was the gas cap!