For mass gaining, we very well know that carbohydrates are needed.
The point is: which ones?
If you like eating some sweets and wake up early in the morning to workout or go to job, then it is much better to switch the carbs intake to the morning. Replace the rice and cereals of the dinner/lunch with all you need in the morning. Glicemia will be under control, because you have a whole day to burn your carbs.
You can eat without sorrows 1) cornetto and brioches (better with egg cream or Honey), 2) good cereals and legumes biscuits.
I love adding grated coconut with chestnut honey to a void vegan cornetto.
For lunch/dinner, Avoid potatoes. They will not give you the right energy for workout and need many fats to be cooked and dressed. They also make you sleep and slow metabolism down.
If you can, replace common rice with farro. It’s a cereal rich in fosforo, high in fiber, with great row taste, for combination with fish and veggies. It has gluten, but not that much. It is fine for brain.
Find here the recipes to traditional cornetto
If you like the salty potatoes taste, then, do not buy fried ones, but cut them into thin slices and put them on a hot pan for some minutes. Add salt, sesame oil and pfeffer/red hot chili at the end. Mix with some salty peanuts. You will have your healthy ROASTED potatoes chips. Add some roasted oat flakes to make it crunchy and complete. Oat is usually used with sweets, but it is fine with salt and eggs in salty version. Better oat than rice for mass gaining.