Place eggs in a large saucepan and cover with cold water by 1 inch. Bring to a boil and cook for 1 minute. Cover eggs with a tight-fitting lid and remove from heat; set aside for 8-10 minutes.
Cool eggs in a bowl of ice water for 2-5 minutes. Drain well and peel; cut the eggs in half lengthwise, reserving the yolks.
Heat a large cast iron skillet over medium high heat. Add bacon and cook until brown and crispy, about 6-8 minutes. Transfer to a paper towel-lined plate; set aside.
In a small bowl, mash the yolks and avocado with a fork until chunky. Stir in cilantro, lemon juice and lemon zest; season with salt and pepper, to taste.
Use a pastry bag to pipe into the eggs, topped with bacon and garnished with chives and cayenne pepper, if desired.
Notes
Older eggs are easier to peel. Older eggs will generally be much easier to peel than fresh eggs. The higher pH of the older eggs allows the whites to separate from the inner shell membrane, making it that much easier to peel.
Use an ice water bath. Immediately cool the eggs in an ice water bath for 5 minutes, halting the cooking process and preventing overcooked yolks (and whites).
Try the pressure cooker for hard boiled eggs. For the most perfect, consistent and easy-to-peel hard boiled eggs, use the Instant Pot instead.
Use a pastry bag for the filling. A pastry or piping bag can help fill the egg whites uniformly and consistently with less mess and less time. A Ziploc bag with the corner snipped off can also work as a pastry bag. Use a piping tip (1M, an open star pastry tip is used here) for more decorative patterns and a picture-perfect finish.
Mix it up. Use lime juice instead of lemon juice, add red onion for a pop of color (and a little bit of crunch) or add Sriracha for an extra kick of heat.