You could replace meat with lentils!! It's a better alternative....
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.