Dharma, just leave out the walnuts altogether...
actually that is my own addition to the original recipe...
raisins or currents or dried cranberries would also be a good substitution...
Remember, any recipe is just a stencil, you fill in the lines yourself... experiment with your own changes from there~!

I'm not a big fan of Kashi myself, BUT Grape Nuts sound wonderful!
I'd sprinkle them on top at the end, rather than cooking them into the mixture...

Final product should look something like this: