To avoid cutting through the seeds and pith, slice from one curve to another.
See? No seeds!
Start again, slicing through the next curve, and so on.
You can try to bend your knife a little bit as you slice to make sure you don't touch the seeds.
You should be able to cut throught the whole pepper with only 4 cuts.
Now just throw away the core! Some people like to cut off the top of the pepper first, but I prefer this method as it doesn't waste anything. Hope you like it!