When turning instant soup into liquid soup, how can I optimise dissolution?
Add the water incrementally. It's probably enough to add just a bit, stir, then add the rest, but you can break it up a bit more if that doesn't work.

A clump of powder or a lump of paste won't dissolve easily into water, but it's easy enough to add a little water to it and thin it out. So the idea is to work your way up from powder to paste to thinner paste to liquid. This is a good idea for all kinds of things where you start with a powder or a thick paste, not just instant soup.