Green onions, or scallions, are probably the easiest things you can grow at home. How to grow green onions at home? Well you can actually grow them from kitchen scraps.
All you need to do is to place a bunch of scallions with their roots in a glass full of water, then place in a sunny window. Cut off what you need to use in your cooking and the onions will literally regrow themselves almost overnight. Read more details at 17 apart here.