I remember reading about an easy recipe on the Australian vegetarian society website about mixing a can of lentils and a jar of pasta sauce and heating it up in the microwave or a saucepan. Boil some wholegrain or veggie pasta to go with it.
Another easy meal is to get a can of baked beans (don't know if other countries have them) and spread them out on a couple slices of bread and bake it.
It's easy to turn most recipes vegetarian by simply adding beans or lentils instead of meat.