Take the yakisoba noodles out of the bag and place in a microwave safe bowl. Lightly cover the bowl with plastic wrap and microwave for 2 minutes.
After microwaving and allowing the yakisoba to cool down, place the yakisoba in a Ziploc bag or a plastic bag. Pour in the mackerel in juices in the bag and mix well. Rub the bag to ensure that the yakisoba is covered entirely.
Pour the yakisoba on a plate and top with green onions. You are done!