Nuts are rich in oil, which is one reason they are so high in calories. How about other fat rich foods you may like. ice cream, cakes, chips, crisps, toast and butter, crumpets. If you need to build your weight up, I think you can forget about nutrition, calories are all.
DGS, aged 7 and a skinny lad at the best of times recently had a severe virus infection, lost his appetite and lost 7lbs in weight. I normally never give DGC sweets, except Easter and Christmas but I rang DDiL and suggested that a food parcel of chocolate might help him and she totally agreed, so i am supplying regular chocolate to get his weight back up.