I cook a lot of whole pot dishes, so my method is to cook all the other stuff (onion, garlic, chiles, chicken, plus whatever ground spices or whatever go in to flavor it all), then toss a handful of spinach on right at the end, put the lid on, and let it steam just a bit (until it just starts to turn that beautiful deep green), then stir it in, eat. It doesn't get totally mushy and army green and tasteless that way.
If you want it to totally disappear, get your raw spinach, roll it up into a cigar and chop it up really fine. It will disappear into whatever you put it in.
Or like dude said, eat it raw or just dipped in boiling water, then rinsed in ice water.