Place the eggs in a single layer in a large pot. Fill the pot with water until it is about ½ inch above the eggs.
Bring the water to a boil. Then, cover the pot and remove it from the heat. Let the eggs sit in the hot water for 14 minutes. Meanwhile, prepare a large bowl with ice water.
When the eggs are finished, use a slotted spoon to transfer them to the ice water bath. Let them cool for 1–2 minutes, then peel them under water. Pat the peeled eggs dry with a paper towel and chop them into small pieces.
Add the chopped eggs to a large mixing bowl. Stir in the mayonnaise, mustard, celery seed, paprika, kosher salt, black pepper, and green onion until evenly combined.
Scoop about 1 cup of egg salad onto your choice of bread or croissant. Add optional toppings such as lettuce or tomato, if desired.