DIY frozen meals?

I've been subscribed to a meal service which sends frozen, pre-made meals which are designed to be microwaved in the morning and put in a thermos to eat for lunch. It's kind of expensive so I'm wondering if there's a simple way to make these kinds of frozen meals myself. They are usually a variety of veggies and a protein with a sauce (I think they're intended to be eaten with rice but that's one too many steps for me lol). Since I can get lots of frozen ingredients at my local supermarket, I'm thinking I can just mix some veggies and protein in a bag, and then microwave it with some... sauce? Does this seem like it would be effective, or do I need to cook the whole meal together before freezing it?