Try a dressing with avocado, low-fat plain yogurt, a bunch of herbs, fresh lime, etc. It won't be an oil-based dressing and does contain some fat, but avocadoes contain good fat. Also, make a peanut-based dressing - just do some research for healthy ones!
I also recommend making MORE food at dinner time (a variety of healthy dishes) so that you have stuff to take to work with you. For example, I'll make delicious pork loin, chicken breasts, fish, etc. for dinner, with an extra large salad so we have leftovers. Try different recipes like this one:
http://www.epicurious.com/recipes/food/views/Black-Bean-and-Rice-Salad-2369
Just don't cook it with rice. I make the salad alone - such a nice combination with any meat you want! If you need the rice, use brown rice, of course! A little preparation goes a long way - that way, you don't need to eat canned meat all the time (yuck) or get bored with your salads. Explore the Internet for new recipes - you can always adapt them if they contain bad ingredients! Whoever said healthy food doesn't taste good - hogwash! It's ALL about how you cook it and what spices you use. I like to use different cookware, too: steamer, crockpot, bake, grill...mix it up!
Oh, and healthy snacks. With some extra snacks spread out over the day (little cheese nibbles, cherry tomatoes, can of tomato juice, cucumber slices, meat and lettuce roll-ups, etc.), you won't even miss crappy carb-filled lunches! I don't feel hungry until after I come home from the gym after work now.