Can't provide recipes per se, but there are a lot of normal—and even healthy—foods that can help to gain, as long as they are calorie-dense and high in carbs and/or fat:
-nuts (peanuts, almonds, etc)
-whole wheat bread, bagels
-chicken (thighs, breasts, etc)
-any fatty meat (beef, pork, etc)
-potatoes
-beans (baked, pinto, etc)
-whole milk, full-fat yogurt
-cheese
-most fruits (including dried, i.e. raisins)
-fruit juices
-granola
The list goes on and on. Buying foods like these are also usually cheaper than buying junk food (in terms of calories-per-dollar), though obviously they're good too as caloric supplements. Study up on which foods you like and can fit in your budget and you should be all set. Most online articles about gaining weight healthily will include lists like the one above that suggest good foods for gaining. Here's one, for example:
authoritynutrition.com/how-to-gain-weight/They're usually written for underweight people, but the principles are the same; just on a larger scale depending on how much/quickly you want to gain.
As for hiding unhealthy stuff from parents (for which I accept no responsibility if it doesn't work
): get an opaque plastic container that's big enough to hold a food stash but that can also be tucked away and inconspicuous when necessary. Worked for me back in the day, anyway.
Hope some of that info can help. Happy gaining!