There are two kinds of precut onions you can buy - refrigerated in the produce section and frozen in the frozen vegetables section. Also, TJ offers refrigerated Mire Poix - precut onions, carrots, and celery. I know all of that because I simply cannot chop onions without crying! I sometimes would buy leeks, that have an even better taste than regular onions without any crying.

You mentioned yummy casseroles... this reminds me that I have a crock pot. A good idea...