Pound the chicken breasts to an even thickness with the bottom of a mason jar.
Combine chicken with cajun seasoning in a bowl. Toss to combine.
Heat a frying pan large enough to fit the chicken in a single layer over medium-high heat.
When the pan is quite hot, add the olive oil and seasoned chicken. Cook undisturbed for just about 1 minute to help them get a little golden on one side (you are not actually searing or browning them).
Flip each chicken breast over.
Reduce the heat to low.
Cover the pan with a tight-fitting lid. Set a timer for 10 minutes, and walk away. Do not lift the lid; do not peek.
After 10 minutes have elapsed, turn off the heat. (If you have an electric stove, remove the pan from the heat.) Reset the timer for 10 minutes and leave the chicken breasts in the pan. Again, do not lift the lid; do not peek.
After the 10 minutes are up, uncover, and your chicken is done. Make sure there is no pink in the middle of the chicken breasts. If you want to be absolutely sure it is cooked, you can use an instant-read thermometer to check -- the chicken should be at least 165°F.
Transfer cooked chicken to a clean plate, and slice.