@Brian1946, just about anything. Often it’s some little amount left over from a meal. A few sauteed mushrooms, a handful of peas, some zucchini or broccoli, whatever. If it’s big, I chop it up. Usually if I have some fresh onion I’ll chop it well and put it into the water at the start.
A sliced hard-boiled egg is another welcome addition.
For things already cooked, I’ll wait until nearly done and add to the boiling water. I do like to include raw spinach, chopped a little, which I’ll just put into the bowl before pouring the broth and noodles in. That’s enough time and heat to cook it just slightly, so it’s not crunchy.
@longgone, stirred in, dissolved, and creamy, or just a lump or a bunch of little lumps? Not picturing it.