Spray each mason jar generously with non-stick oil spray.
Add chopped green onions and cheese to each mason jar (you can customize with your favorite ingredients), filling about 1/3 full.
In a large measuring cup, whisk together eggs, salt, and pepper.
Pour the egg mixture to the jar, leaving about 1/2 inch from the top. (If you don't pour enough mixture to the jar, the mason jars may float in the water bath.)
Close the lid “fingertip tight”. (You can easily open with 2 fingers).
Fill the container or pot with water and set the temperature of the sous vide circulator to 172°F (73°C). (Place a trivet mat beneath the pot to help protect your countertop!)
Place the mason jars in the water before the water gets hot. Set the timer for 1 hour.
When the timer goes off, remove the jars from the water, and let cool for about 10 minutes.
Run a knife around the edges of each jar to loosen. Remove them from the jars and serve warm immediately (or freeze for meal prep).