If you've got an available microwave, there are few lunches as satisfying as frozen pasta dishes. I've found good (and bad) inexpensive Italian dishes in the freezer case at the supermarket, and there are a couple of brands that I know will almost always be good enough to buy more than once.
Celentano is one of these brands. I've mentioned their eggplant parmesan as one of my regular choices, and their lasagna is one brand in a three-way tie for best in a comparison of eleven different varieties I taste-tested a few years ago.
Stuffed shells are the perfect lunch for someone who loves ricotta cheese, and Celentano delivers in a big way. The freezer tray you buy contains six jumbo pasta shells, plump with seasoned ricotta stuffing, dressed with Celentano's delicious-though-basic tomato sauce. If you're wicked hungry, you won't have any problem eating all six shells. If your appetite is lighter and you're having lunch with a friend, you can have three each and a small salad and you're good until supper time. And if you're a Mom-Dad-and-Junior nuclear family, you can dish out two each as a side dish with, say, oven-roasted chicken breasts and a tossed salad.
Any way you decide to go with these stuffed shells, you won't go wrong. They're great.