The bass riff (arranged for guitar) is fairly easy.
The lead part is mostly based around the 2nd shape of A minor pentatonic. It’s mostly sparse, so it’s easy to play if you can do it by ear. If you have trouble with the faster parts — slow it down!
Note that the lead score is on the bass tab. (Yes, I should have done it the other way round!).
Here’s the powertab file for Greenish Onions.