How do I plant scallions in an egg carton?

I grow then in pots in my back yard.

Have never done this, but you could give it a try. Mine are in a raised bed.

This would be only to get the germination of the seeds started. Once the seedlings were visible above the surface of the soil, they would need to be transplanted into deeper soil, in pots, or in a garden. The depth and size of the egg carton indentations would not be sufficient enough to provide adequate space for the roots to grow into maturity.

This shows how to plant green onion in an egg carton: https://www.youtube.com/watch?v=Utu7JCDuAoA

This also shows how to grow scallion: https://www.youtube.com/watch?v=HX9a45xyugY

This is a good tutorial: https://diyjoy.com/how-to-grow-green-onions-at-home/

This is another helpful tutorial: https://www.amazevegegarden.com/how-to-grow-onions-using-an-egg-carton/