Another thing that comes to mind is that places like Amazon sell sets of food portion trays with lids - they could possibly make their meals in advance for the following week, so they only have to cook them at once and can just warm them up in the microwave as needed. In particular, I've noticed a lot of bodybuilders doing this on Youtube, they will buy some chicken breasts in bulk from their local butcher, then marinate them and throw them all on the grill at once. Then they will assemble them into these portion containers with something like baked sweet potatoes, and perhaps a topping like some salsa or some roasted vegetables. In fact, one of the other benefits they mentioned about using these trays is that due to their size, no matter what you put in there it's generally only going to be around 300-350 calories. Of course if you fill the whole tray with something like mayonnaise, that's not going to be the case, but I'm talking stuff like pasta or a sandwich, etc...