How to gain weight gluten-free?

Gluten-free: You can add more protein, and starches that are not wheat-based. Sweet potatoes, brown rice, quinoa, various squashes, etc are fine, for instance. Eat fruits unless concerned about Insulin resistance. Also add healthy oils like coconut oil, olive oil. Eat larger portions and be physically active, including exercise with weights. You want the weight you gain, to be muscle rather than fat.