If you have a bunch of egg cartons with punched holes in the bottom, for drainage. Cut out a panel from the lid on three sides, so you have a flap of sorts on top. Then Fill the bottom half of the cartons with potting soil, and then put in enough seed starting medium on top for the seedlings to emerge into.
After that Put in your seeds, one future-plant per cell. Close the flap on top to keep in moisture while the seeds are germinating. Once they’re up, rip off those top panels and stick the cartons under lights to grow until the garden is ready for them.