Question: I'm vegan and in general I don't have any problem maintaining my weight, but for the last few months I've wanted to increase my weight and it's been really hard. 

Could others who have had the same problem give me some tips or advice on how to gain weight on a vegan diet?

Answer: 
My **#1** tip: **drink calories**

If I want to gain weight, I make a smoothie with two bananas, a generous scoop of nut butter, vegan milk, and a tablespoon of carob. I drink this alongside my normal breakfast. I typically gain about 4kg per month doing this.

Turning food into drink by way of smoothies should enable you to eat more calorie-dense food easily.
Oatmeal, bananas, potatoes and soya beans have a high calorie content. Nuts and seeds often have a high fat content, which translates to a high calorific value. If you eat more calories than you use, you gain weight, so these are all good options.

Then there's exercise, muscles are denser than fat, so if you build up your muscles you'll weigh more.