It's a common misconception that humans need a lot of meat to be healthy. Many people around the world are vegetarian and they're perfectly fine -- heck, they're usually healthier than the folks who eat greasy burgers all the time. The problem is that if you just remove all the meat from your diet and eat nothing but French fries and lettuce salad ... Um, yeah, of course you'll get sick. There's no nutritional density there.
A balanced vegetarian diet has stuff like beans, lentils, soy, whole grains, nuts and seeds to provide protein and vitamins. Milk and eggs are optional. And it's important to get lots of colourful fruit and vegetables (red, orange, yellow and dark green). Even the much-maligned potato is healthy as long as you eat the skin and, y'know, don't drown it in butter and grease.
Heh, I'm actually not a vegetarian myself. Animals are too delicious. But I use vegetarian ideas to help me cook healthier and keep my meals interesting. Sometimes I'll cook, say, a big pot of barley, kale and sweet potato with just a little bit of bacon for flavour.
I'd suggest researching world cuisines, though. Indian food, for example, has lots of vegetarian dishes with flavourful curry-type sauces. It's probably easier to find an Indian take-out restaurant than to find a hamburger joint with a decent veggie burger!