Remove yolk from hard boiled eggs and place in a medium bowl. Mash yolk with a fork until crumbly. Set aside.
Slice avocados in half lengthwise, remove pit and scoop out the flesh with a spoon into a small bowl. Mash avocado with a fork.
Spoon mashed avocado into the bowl with the mashed yolks. Drizzle as evenly as possible with lime juice.
Add red onion, sour cream, garlic, cumin, salt and pepper and stir well to combine.
Place yolk mixture in a piping bag or a plastic storage bag (if placing in a plastic storage bag, place in a corner of the bag and cut the corner tip off of the bag).
Squeeze mixture into the egg whites.
Top with fresh chopped cilantro, chili powder and/or sliced serrano peppers.