There are many good vegetarian protein sources. Nuts, beans, higher protein whole grains and seeds and grain-like foods. I'd go buy a few books on vegetarian cooking. But know that not everyone is equipped to do well as a vegetarian -- most vegetarians do it for ideological reasons and it is harder to get all your nutrients as a vegetarian, particularly methionine and B12, so you do have to learn how to do it well. Food groups don't differ for vegetarians and meat eaters, just the source of protein does.
You could replace meat with lentils!! It's a better alternative....