When it comes to cheap and easy vegetarian recipes, you can't do much better than fried rice. It's quick, simple, and versatile - you can add just about anything you want to a batch of fried rice, and it will be quite tasty.
Here's a tip for making fried rice - whenever you are making a rice based dish, cook an extra 1 1/2 cups of rice - this will make an extra 3 cups when cooked. Put the extra cooked rice in a plastic food storage bag and throw it in the freezer. That way, you'll always have a base for a fried rice meal - this can be wonderful for those nights when you just don't have much time to cook.
Here's just one of the endless variations of fried rice that you can throw together in under 15 minutes:
3 cups cooked rice
2 tbsp sesame oil or olive oil
1 carrot, cut into 1/2 inch strips
2 stalks celery, chopped
1 medium onion, chopped
1/4 cup soy sauce
1 tsp hot chili sauce
8 oz tofu (bean curd), cut into 1/4" x 1/2 inch pieces
Heat oil in a large skillet or wok. Add cooked rice, stir fry for 2 minutes. Add tofu and soy sauce, stir fry for another 2 minutes. Add remainder of ingredients, stir fry for 5 minutes or until vegetables are tender.
Serve with spring rolls or vegan hot and sour soup.