Add a rack to the center of your oven and preheat it to 400°F. Pound the chicken breast an inch thick with a heavy skillet. Sprinkle liberally on both sides with taco seasoning.
Add cooking oil to a heavy-bottomed skillet set over medium-high heat. Sear the chicken breast for 5 minutes, then flip it and cook for a few minutes more, or until a thermometer reads 165°F.
Slice the jalapeño and two green onions. Chop the cilantro. Dice the avocado and drizzle lime juice over it to keep it from browning.
When your chicken has reached an internal temperature of 165°F, remove it from the pan and let it rest for five minutes. Chop it into 1/2-inch pieces.
Line a sheet pan with parchment paper. Add half a bag of corn chips to the pan. Top with half of the shredded cheese and half of the chopped chicken.
Repeat the layering process with the remaining chips, cheese, and chicken. Bake at 400°F until the cheese melts, about 7 to 10 minutes.
Sprinkle the nachos with the avocado, jalapeño, green onion, lime zest, and chopped cilantro. Finish with dollops of sour cream and sprinkle with crumbled queso fresco.