Marinate chicken: At least 1 hour ahead of time, marinate chicken. Slice chicken breasts in half (to thin out). You can also cut the chicken into smaller pieces if the chicken breast halves are large. Place the chicken in a single layer in a zip-top bag and pound with a tenderizer so that all of the pieces are about 1/2" thick. Add buttermilk and lemon zest to chicken. Refrigerate for at least 1 hour minutes and up to a day.

Heat oven to 400 degrees F.

Place an oven-safe cooling rack on top of a sheet pan. (You can also bake these directly on the sheet pan, but the cooling rack will allow some air to circulate underneath and give it maxim crispiness on both sides.)

In a sturdy plastic bag, combine cornflakes, salt, thyme, paprika, garlic powder, and pepper. Seal the bag and use a rolling pin or other flat-bottomed tool to crush the cornflakes until the largest pieces are about the size of a pea. (You don't want to create a powder, so make sure that some small pieces remain.

Remove chicken from buttermilk, shake off the excess liquid, and transfer chicken to the bag with the cornflake mixture. (I like to do this over the sink since it can get messy.)

Working with one piece of chicken at a time, firmly press it into the cornflake mixture. Try to pick up as much of the cornflake mixture as possible.

Set the chicken on top of the prepared baking sheet. Repeat with all remaining chicken.

Finally (don't skip this step), use your hands to scoop any remaining cornflake mixture out of the bag and sprinkle it over top of the chicken peices. (This will insure that you get all of the spice mixture and any remaining small bits of cornflakes onto the chicken.)

Drizzle the tops of the chicken with cooking oil (this will help it to brown / crisp in the oven).

Immediately transfer the chicken to the oven.

Bake until the chicken is cooked through and registers 165 degrees in the middle, 13 to 17 minutes.