Using a meat mallet, place the chicken between pieces of wax paper and pound out each chicken breast so they are an even width.
Bring the oil (or butter or cooking spray) to heat over high heat in a skillet.
When the oil starts to shimmer and smoke, add the chicken. It should pop and sizzle.
Immedieatly turn the heat down to low and cook for 5-7 minutes. *See note
When the chicken is white halfway up the chicken breast, flip it and cook an additional 5-7 minutes. *See note
Remove the chicken to a cutting board for 1-3 minutes to rest.
* The most important thing you are looking for is to get down and look at the side of the chicken. Once it is white, and cooked through halfway up the chicken, flip it over. When there is no longer a pink rim around the edges of the chicken it's thoroughly cooked.