1 1/2 cups of oats in the gainer is overkill.
3/4 cup oats still has good macro profile with plenty of calories and you can get it down pretty easily.
although if you don't have the time to make your own weight gainer i'd recommend Cyto Gainer or Prolab N-Large 2 I've had both and was happy...
Marijuana is different for everyone. I don't think it gives everyone the munchies, although it probably depends on the strand.
In addition to Megace, doctors prescribe Periactin Appetite Stimulant - which has shown to be very effective to stimulate appetite in underweight people. It is a type...
It's not really a question of what is healthier. The goal is to add mass. Some people, especially hardgainers, struggle with eating the required calories, so weight gainers make it a bit more convenient to meet their calorie goals.
The only suggestions in this thread were basically nuts and fats. You can hardly base a diet on just these two things, so was throwing more ideas out there :)
You want to eat lots of calorie dense foods which include complex carbs (pasta/rice/potatoes/whole grains), protein supplements, and "healthy" fats including flaxseed oil, avocados. More high calorie foods are listed here http://www.gainingweight.info/healthy-high-calorie-foods-to-gain-weight/