What facilities do you have at work?
I WFH now but back when I worked in the office and was dieting a food thermos was my saviour.
If you cook up 500g 5% fat beef mince with a tin of tomatoes, tin of sliced carrots, couple of chopped onions, couple of punnets of baby button mushrooms and whatever seasoning pack you like (chilli, shepherds pie, bolognaise...) it makes 4 generous portions and gives you a decent amount of protein and fibre but low carb and a couple of portions of veg per serving. I'd get that really hot in the morning, preheat the food flask by putting boiling water in it for at least 5 mins then fill it. The flask kept it hot till lunch time. Each portion is about 220calories
If you have a microwave at work you can make scrambled egg (depending on how sensitive colleagues are to the smell), just put a couple of eggs still in shell into a Tupperware with any seasoning, veg, cheese etc you usually add, then at lunch just crack the eggs, give it a stir and cook it in 1 min blasts stirring in between till it's the consistency you like.
Warm salad was another favourite, put prepped veg - mushrooms, green beans, sugar snap peas, asparagus, tenderstem broccoli etc into a Tupperware with a knob of butter and some seasoning. In another pot take some wafer thin ham, chicken or a sliced boiled egg. At lunch just take the lid off and put it loosely over the top of the Tupperware so there's room for steam to escape then microwave for 3 mins to steam the veg and melt the butter, stir in the meat or egg and enjoy. About 200 cals depending on amount of butter and meat/egg.