I definitely would not consume quinoa because when I ate it, I couldn’t digest it at all. Its a tough item for your body to process and has been a widespread problem on the forum since I’ve been here for the last 2 years. Buckwheat is a much better alternative in general.
If you are looking for a great weight gain food, I would look no further than teff:
Incredibly nutritious, similar to wheat but has no gluten, tastes good, gives you power and strength, prebiotic that feeds the probiotics…so many good things about it.
As you rebuild your gut flora, you’ll have a greater surface area inside the gut to absorb the food, so you should be able to gain weight in time. Additionally, if you get proper nutrition, your body will be able to grow better.