Salsa chicken without using salsa from a jar?

The jar salsa in NZ isn't the greatest stuff. Maybe after hours in a slow cooker it might be ok, but is there anyway of making my own style, by say adding tomatoes and onions to the slow cookers at the start? Or is that doomed to fail.

I've only ever made stews with beef in my slow cooker so far, so I'm an but unsure of what would happen!

Thanks