I'm exactly the same, normally love soup for lunch and it's so easy!
I've been making couscous salads, I buy those bags of frozen mediterranean veg and put some of that in along with cherry tomatoes. To keep the couscous full of flavour I add harrisa paste (I finally found this after searching in a small jar near the stuff like olives/roasted peppers etc) to the stock I make it with, yum. I normally make a load and pack up 3-4 lunch boxes to keep in the fridge and it does seem to keep well.
For a nice lazy option, sorry it's a salad but it's yummy. I buy these £1 simple salads from tesco, you find them with the bags of salad leaves and they contain mostly lettuce with a few cherry toms, slices of cucumber and radish. I also buy a £1 tub of prawn in marie rose dressing, the light one has 210 calories and tastes really nice and creamy! Just like soup you can just buy this and deal with it at work.
For a different salad I like chopped up raw veg; carrot, red cabbage, broccoli and pepper along with cherry tomatoes. Some balsamic/olive oil dressing and sometimes put reduced fat feta in this too. It does take a bit of time because you do need to slice up the veggies quite thin.
I need more ideas though so this is great- I love the sushi idea! Thanks!