The lunch sounds fine for 8 YOs, or anyone else. You do not need bread, or meat or whatever to make it a meal.
However, as some have pointed out, is likely to be about 700 calories, which is quite a lot for just one meal, and also demonstrates that cold food is not necessarily 'lighter' or less.
There are any number of hot, cooked meals that can be loads less than 700 calories, and certainly if you are on something like a Slimming World type diet, apart from salads, it is quite hard to eat cold food, because things like sandwiches are heavily restricted. Hot meals can be things like meat and veg in sauce, roast dinners with lots of veg, or chilli with lots of beans and veg, so not unhealthy and lacking in vegetables.
I much prefer hot food and eat 2 or 3 hot meals each day. Some of these are simple light meals like soup, or eggs or beans on toast, or omelettes and a lot are leftovers, or reincarnations of leftovers (eg chilli and rice, and then burritos using leftover chilli), so its not faffy, or hard work.
I am not overweight and don't eat more because I mostly eat hot food. I just very much prefer to have, for example, a cheese toastie or a slice of pizza, rather than a cheese sandwich.
My ideal 'lunch on the run' is a carvery, which if you stick to mostly meat and veg, and don't go mad on stuffing/roasties/yorkshire puddings is much healthier than sandwiches or similar.
I accept that others prefer different, and that's just it, preferences. Ironically, one of my siblings hasn't eaten a vegetable or cooked meal in at least 10 years, eating only sandwiches, biscuits, cakes and chocolate.