Place eggs in a saucepan, cover with water, and bring to a boil. Cook for 10 minutes.
Transfer eggs to cold water, peel, and chop into small pieces.
In a bowl, combine chopped eggs, mayonnaise, Dijon mustard, celery, and chives.
Season with salt and black pepper, then mix until thick and slightly chunky.
Slice avocados in half and remove the pits.
If needed, scoop out a small amount of avocado to create more space for filling.
Spoon the egg salad evenly into each avocado half.
Serve immediately or chill briefly before serving.