I buy organic beef mini meatballs from the supermarket, which makes this extremely easy to put together, and there'd be nothing to stop you freezing them and cooking straight from frozen, if that helps. In which case, I'd just pop them in hot sauce and not attempt to brown them first.
Sure you can make your own meatballs, but so long as you're happy with the provenance of the meat (which is always, always important), don't beat yourself up about cutting it at this stage, when you know everyone's going to be happy come suppertime. Likewise the packet of diced veg: once everything's swimming in its mellow sauce, no one is going to be asking questions.
Recipe posted by Nigella