You are displaying your lack of knowledge here: burgers, as with most food ingredients, have zero VAT as a purchase. Whilst I've no doubt that there are some operations who do what you're suggesting, in practice, it would be very hard to operate without a very significant risk of getting caught. You'd need a whole supply chain to be complicit. You'd have to ring some sales up through whatever POS system you’re running, but not others. You'd need staff to cooperate. Your (declared) turnover would not have to be too far off comparable businesses to avoid raising a flag with Revenue (they can and do monitor such things in particular sectors). It's hard enough to keep one set of books without having to keep two parallel ones. You might get away with it for a while, but the chances are you'd end up being audited, either because your own returns had been flagged, or one through an audit of one of your suppliers. I'm not saying it doesn't happen - it clearly does, as published Revenue lists prove - but I would not underestimate the difficulty in doing as you suggest and getting away with it for any length.
The interesting point about this thread is of course that it's an evidence free zone, so I guess my opinion is as valid as anything here. For what it's worth, I think it likely the only sector where evasion is likely to be significant is where small operators are selling services to end consumers. Anyone part of a supply chain would find it very difficult to keep it up for any length of time. Of course, the really big evaders are likely to be those in the murky place where aggressive avoidance meets evasion.