Yes, they're in the frozen section, but they're frequently in a 'special' section for vegetarian stuff. . . but veggie burgers, Quorn products, faux chicken nuggets, and stuff like that.
I know about these because I've been vegetarian for 12 years, but they're a good adjunct for anyone's diet. It's not animal protein, so it's easier to provide macronutrient balances favoring protein without so much fat. Mileage may vary based on product, so read your labels.
Also, some are nasty, and some are great. Morningstar Farms does well by me for all their products. I REALLY like the Quorn products, but the breading on the chicken nuggest can be too much if you're cutting carbs. The various veggie burgers vary widely in flavor and ability to simulate meat (some of the best tasting aren't necessarily trying too hard to simulate meat), and they all have a favorable protein/fat ratio when compared to ground beef. They can be a bit pricey, thoguh.