Hard boil eggs. Peel under cold water and cut lengthwise in half
Transfer yolks to bowl. Cover and chill yolks and egg whites seperately for one hour. In a large bowl mash the yolks with a fork and set aside.
In a separate bowl mash the avocado into a paste-like texture (lumps are ok), then stir in lemon juice. Combine mashed yolk and avocado together.
Mash in the mayo and ground mustard stir until well blended - add salt and mayo till desired taste/consistency
Place yolk mixture in plastic sealable bag. Cut small corner out of the plastic bag. Squeeze the yolk mixture out to fill the egg white halves.
Cover and refrigerate until ready to serve, then garnish with minced chives and crumbled cotija cheese.