Slice the jalapeños lengthwise down the center, taking care to cut through only one side and leaving the pepper as intact as possible. Remove the seeds.
In a large bowl, combine the ground beef, taco seasoning, salt, pepper, and cilantro. Mix to combine.
Heat the olive oil in a large pan over medium heat. Cook the onion for 1 minute, then add garlic and cook another minute.
Add the beef mixture and cook until browned, approximately 5 minutes. Remove from the heat and let cool completely.
In a clean, large bowl, combine the cooled beef mixture, shredded cheese, and cream cheese.
Transfer the beef mixture to a piping bag or zip-top bag with a corner snipped off.
Pipe the beef mixture into the jalapeños, then close the peppers.
Heat a large pot filled with the oil until it reaches 325ºF (170ºC).
Add the seasoned flour, eggs, and cornflakes to 3 separate shallow bowls. Dip the peppers in the egg, then the flour, followed by the egg again, and then the cornflakes. Dip once more in the egg and finish with a second dip in the cornflakes.
Fry the peppers, in batches, for 2½ minutes until golden brown. Remove with a slotted spoon or tongs and drain on a wire cooling rack.
Season the peppers well with salt and fresh lime juice.