What foods should I eat to gain weight?

I'm trying to gain FAT (muscle too, but mainly fat) because I am 5'8" and only 104 lbs. I am a size 0 and I am bony! It even hurts to sit or lay down in certain positions because of my bones poking out.
Even though I am underweight, my doctor says i'm healthy. My lab results always come back great...I have no nutrient deficiencies or health problems. But even though I am healthy, my doctor said that i AM underweight and that I should try gaining some weight to prevent myself from developing health problems in the future. He suggested that I eat some meat, eggs, or dairy. He said that animal fat would help me gain weight. But I am vegan and NOT willing to eat meat or eggs or dairy. Is there any VEGAN food that will make me gain weight? I already eat A LOT and nothing I do works!! I snack on fruits all day long, I eat HUGE portions of food for my meals, and I eat a lot of CARBS. For lunch today I had a huge bowl of steamed white rice (i had so much in my bowl, it was a mountain of rice overflowing the bowl), a separate huge bowl of black beans, and a separate huge bowl of steamed brocolli. I eat this much for EVERY meal. I literally eat til I am stuffed and can barely breathe. What vegan healthy food can I eat that will make me gain weight? What I mean by healthy is that its not heavily processed with a bunch of unnatural ingredients and high in sodium, etc. I eat only natural foods that are mostly organic.