As your hba1c is excellent, I would say try eating 1 extra CP at each meal and cover it with insulin.
Do weight training and try eating protein within 20 minutes after your workout to promote muscle build up. You can try a shake too if you like - protein/creatine stuff if you don't have any complications to consider.
Eat more healthy fat - fatty fish, olive oil, almonds...
I am doing the 2nd bit myself, but as I am trying to lose weight, I do the opposite of advise 1 myself, so I am guessing if you want to put on weight, you'd want to look to carbs. I am losing weight while continuing with the 3rd bit, I always did that. Insulin is fat storing - so take more insulin, eat carbs to cover the extra insulin...
I would rather be any weight with a sensible muscle mass myself than have too much body fat, but if you don't have enough then I would try above. You can work out your fat percentage from one of the applications online - measuring tape, your weight and height will give you a good guess.