Well, I know you say you don't have time to get to the gym, but that is what will boost your appetite and help build the muscle you're looking for. Even if you can't do it regularly, try to at least go for a jog around your block once or twice a week or do workout videos (like the well-known P90X videos) that are quick to whip you into shape at home.
As for meal plans, combining complex carbs and protein is your best bet for gaining muscle. Good meal choices are eggs and whole wheat toast with, lean meats with baked potatoes or whole grain rice/pasta (veggies don't hurt either ;-)), and protein bars/shakes with banana or peanut butter as snacks in between. The trick is to sneak in calories where you can. On the days that you hectic schedule doesn't leave you much time to cook, meal replacement shakes will be a big help.
Here's a good link: http://ca.askmen.com/sports/bodybuilding/45_fitness_tip.html
All the best.
Only want to say, those foods are used successfully by bodybuilders, bu they aren't good for you. Now, bodybuilders will consume pretty much anything that gives them big muscles, but those shakes and potatoes and all that pasta will help you gain weight because of the high sugar metabolism, but if you aren't lifting weights to exhaustion they won't do anything but give you flab. Obviously, to gain weight, eat more, and to make it muscle, do resistance training of some kind in a careful way, but gaining weight in an unhealthy fashion will come back to haunt you later. I think you need to read up on nutrition -- there's so many theories out there, it's good to see what several people have to say and divide by two. But a basic healthy diet balances protein with lots of colored vegetables and whole grains, preferably not just wheat, which is problematic to digest. To gain weight eating the same healthy diet anyone should eat, just eat an additional meal, and resistance training will help put on muscle. Good luck.