Can you make goulash using winter squash instead of cabbage?
Ok, so as we established in the comments, you don’t need cabbage for goulash. The easiest solution would be to leave it out.
However, goulash is just one version of meat stew. And the principle of stew (with or without meat) is “throw what you have in a pot” - way older than any documented recipe. The flavor profile will also be heavily influenced by the spices used and different cooking cultures have different traditions. If you have goat meat, squash and spring onions and would like to serve them together, go for it. You can call it “stew” or “goulash” just as you see fit. (Especially as you are not going to serve it to guests that may have certain expectations when hearing “goulash”.)
As far as cooking method goes, remember that squash will soften way quicker than cabbage and meat, so either expect it to fully disintegrate (like onions in goulash) or add the pieces later.