How can a teen girl gain one pound a week?

I have been underweight for a while and I am desperately looking to gain some healthy weight on my bones! I am a 16 year old girl who is a vegetarian and I was wondering what kinds of foods should I eat to gain weight/muscle? Also what sort of muscle workouts are there to get more muscle? (i've never had an eating disorder, I'm just naturally thin due to darn genetics!)