What Sarah said. The ingredients are guidelines. Since I've bribed all the recipe police to focus just on people who use mushrooms, you've got lots of room to experiment safely.
I used the soy powder to add a fullness to the taste, and it doesn't really add an Asian flavor, although Mr. Progresso probably used the 3 soy variations in his canned version for thickening - soy proteins, soy protein isolate, and soy lecithin. I don't know what those are, and I probably don't want to know. I like a mild soup so this worked for me and appealed to what I crave at camp on a cool evening.
Next time I'll probably add some parmesan cheese. If my grandfather made this, he'd add a giant spoonful of peanut butter. If my brother made it, he'd throw in salsa. If Sarah isn't watched carefully, she'd probably add mushrooms. And yes, this went great with her pizza muffins. Please post any other variations that are working. Another thought I had is to use this in just its pre-soaked mode as a spread. Just a little more water, and it's stew. Even more, and it's back to being soup. Food is fun!