How do I translate microwave cooking instructions to fanless conventional oven instructions?
Lots of plastic are quite "transparent" to microwaves, but may turn really nasty when exposed to direct heat or the oven (the rest will turn nasty in microwave too; no such thing as oven-safe plastic...)  So, first step - move the meal to oven-safe dishes.

The expected time grows about x6; medium-high heat. Instead of "perforate the film" cover the dish. Remove the cover for the remaining time.

Also, for a lot of "ready to serve, just microwave it" dishes, a skillet is a better choice - unless the dish is "structured" like lasagna, you can get it hot when heating it in a skillet (stirring occasionally) in about 2-3 times the microwave time.