Make the hard-boiled eggs: Fill a large pot with water, add all the eggs, and bring mixture to a boil over high heat. As soon as the water begins to boil, cover with a lid, remove pot from the heat, and let eggs sit for 10 minutes. Drain water and transfer eggs to a bowl of cold water to cool.
When the eggs are cool enough to handle, remove the shells. Slice each egg in half lengthwise. Remove the yolks, adding just 2 whole egg yolks into a medium bowl and discarding the remaining 7 egg yolks. Place the egg white halves onto a platter.
Slice the avocado in half and remove the pit. Use a spoon to scoop the avocado’s flesh into a bowl. Use a fork to mash the egg yolks and the avocado together. Stir in the sour cream and lime juice.
Remove the seeds from the tomatoes with a spoon and discard; finely chop the tomato, along with finely chopping the scallions. Add both to the mashed avocado, along with salt, pepper, and optional jalapeno. Stir together to combine.
Spoon the guacamole into each egg white half, dividing the mixture between all 18. Garnish with a sprinkle of dried or fresh chopped cilantro, if desired. Serve.