Growing up we used to have a salad like this all the time, and it was about the only way I would eat spinach. Still love this combination. I think this particular recipe originated from the side of a bag of mushrooms. I have tweaked it over the years because I don't like to cook the spinach, I prefer to just toss the hot hot dressing over the spinach, which just wilts it enough without cooking it. I'm always throwing bread loaf ends into the freezer, this is a good recipe to use some of them in. Toss the final salad with cheese if you like. Beware, your house will smell like vinegar!!