My standard lunch is a large green salad with whatever kinds of other veggies added, and I chop up and add a whole avocado and a small tin of solid Yellowfin Tuna in olive oil just before eating. With a paring knife in my lunchbag, I can half the avocado, dice up the whole thing while in the shell and then scoop it out with a spoon into the salad. Very little mess. I dress the salad with fresh ground pepper and celery salt before I leave home. The creamy avocado and the olive oil do the rest of the dressing (I'm not fond of vinegary dressings, so that's enough for me.) It's very filling and satiating, keeps me going for hours. I might add a fruit or small yogurt, and tea. Would this work within your work restrictions?