IMO, for prepackaged foods like frozen dinners, the UI should be that you put the food in the oven and close the door, and the microwave figures out the rest. (Of course there would also be manual controls available.)
The simplest way would be with a barcode on the plastic food tray. The barcode would contain the actual cooking instructions so that there's no internet dependency.
But each food company would patent their own barcode retrieval system and put it behind a subscription, only $12.99 for the plan for foods with ads, $24.99 without!
Actually, all implementations would be nearly identical, non-novel, and not patentable. But each one would carry a trademark and microwave manufacturers would charge the TV dinner makers a license fee per meal to put it on the box
The simplest way would be with a barcode on the plastic food tray. The barcode would contain the actual cooking instructions so that there's no internet dependency.