Add pasta to boiling water and follow pasta instructions
Add butter to a pan and fry the onion and mushrooms until soft and brown. You can add a lid to help speed up this process if you're in a time crunch. Remove from pan and add to leftover container of meatballs from the night before.
Add mushroom soup and cream to the pan over medium heat, seasoning with salt and pepper. Heat through.
Once sauce has thickened, add in the onion, mushroom, leftover vegetables and leftover meatballs snipping them in half or smaller with kitchen scissors if you need to stretch the meat portion out further.
Stir through spinach until wilted and serve immediately. If making this ahead of time, add spinach just before serving. See notes for make ahead version.
To elevate this dish, serve with a sprinkle of freshly cracked pepper or dried chilli flakes.