Regarding soup, much of the food mentioned above I've had to let go as too carby. I have small helpings of butternut squash since I managed to grow 15 and am reluctant to give them all away! Onion soup is too sugary and so is tomato soup for me, but some added tomato is ok and home-grown ones I find don't need cooking for long to bring out the sweetness.
Mushroom soup is nice. Bacon bits are good and can be crisped and added at the last minute. Cheese on top is fun especially if it's stringy. Without flour, lentils or other thickening agents I just use my little Mouli hand blender with veg like celeriac instead of potato. Beware of cheap stock cubes and if you can make your own so much the better. Red wine and sherry can add a nice edge.
As for other lunch food, smoked mackerel? You can warm that.
You can make really nice scrambled egg in a microwave if your work colleagues don't mind. Add smoked salmon.
If salads seem a bit chilly, try a sliced beef tomato, olives, basil and maybe anchovies with an olive-oil based dressing warmed (but not hot).
Make almond bread to fill up, and spread pâté or cheese on it.