I tend to live on more ready meals (either frozen or chilled) than I should, although I do manage
some 'proper' cooking too. So I reckon that I'm reasonably knowledgeable on the matter.
The majority of ready meals are either intended to be cooked/heated in a microwave or they're able to be thus heated (even though the end result might not be quites as good as oven cooking). Only a few ready meals are labelled 'not suitable for microwave cooking'.
All of Iceland's products have the cooking instructions available on their website (as well as on the actual packs). Taking the three products you mention as examples, the 'value' lasagne can be microwaved
https://www.iceland.co.uk/p/iceland-beef-lasagne-500g/50820.html
as can the cottage pie
https://www.iceland.co.uk/p/iceland-cottage-pie-500g/50823.html
as well as the bangers and mash
https://www.iceland.co.uk/p/iceland-bangers-and-mash-500g/50825.html
Use the search box at the top of any of those pages to look for other products from Iceland.