Put chicken in medium resealable plastic bag.
Pour buttermilk over and seal the bag. Let soak 6 hours or overnight.
Preheat oven to 450 degrees.
Lightly mist a small, non-stick pan or sheet with spray.
Add the croutons to a plastic bag. Pound them with the flat side of a mallet until crush very fine.
Put the crumbs into a shallow bowl.
Remove chicken breast from the bag and let excess drip off. Dip it into crumbs, rotating it to cover the breast completely.
Place breaded breast onto the prepared sheet so that breasts don't touch.
If crumbs remain, press them into top of remaining breasts.
Lightly spray top of breasts with spray.
Bake for 5 minutes and then carefully, being sure not to remove the coating, flip them.
Lightly mist the tops with spray and continue to bake for 3 to 5 minutes more or until the coating is crisp and chicken is no longer pink inside.