I find the hot/cold thing really strange. As far as nutrition goes, you're much better off eating most vegies raw, and while a hot meal is comforting if you're freezing, I'd assume more often than not the people posting on these threads are eating their dinner inside their heated homes. Where I'm from you just eat what you feel like, regardless of what temperature your other meals of the day were or what temperature it is outside. I do remember my grandparents having a thing about hot food being a meal and cold food being a snack, didn't matter if the hot food contained 200 calories and the cold food contained 2000, but I just assumed that was their own personal weirdness. Guess not!
However, I do find it odd what passes for a 'good meal' in Britain. I would consider a ham and cheese sandwich, beans on toast, plain jacket potato etc. 'can't be fucked' foods, along the same lines as 2 minute noodles. I'm not judging, I eat like that at least once a week because I can't be bothered making something better for myself or because I fed the DC all the healthy stuff left in the fridge, but I know it's a million miles away from ideal.
For me a decent cold dinner would be a big salad with lots of vegies (not just salad leaves), cheese and some form of protein (chicken, chickpeas, lentils). Or some healthy dips, small amount of pita or turkish bread, lot's of raw vegies for dipping, some cheese, maybe a boiled egg and/or some cold meats. Or a big salad sandwich made with naice bread, absolutely brimming with veg. Maybe a cold slice of leftover roast vegie quiche/slice with some salad on the side. None of these meals take long to plate up and you can prepare them in advance, it's just a matter of having access to plenty of veg. It usually takes me a maximum of 5 minutes to put those sorts of meals together for a few people, so still quicker than cooking.
Whatever I'm eating or giving the DC, hot or cold, one meal or lot's of smaller bits and pieces on a plate, generally I'd want to get at least 2, hopefully more like 3-4 serves of fresh veg in at dinner, and if I or they were eating an average British school dinner or the equivalent for lunch, that would become really important because I wouldn't count whatever stodgy potato mess was being served that day as a serve of veg.