Place one chicken breast in a large plastic baggie, and using a meat pounder, pound until about 1/2-inch thick. Repeat with other chicken breasts.
Sprinkle the chicken evenly with salt and pepper.
Spread the flour on a plate.
Coat the chicken cutlets with the flour, shake off any excess.
In a large saute pan, heat the olive oil over medium-high heat.
When the oil is hot, carefully add the chicken. Don't overcrowd the pan.
Cook for about 4 minutes on each side, or until it's golden brown all over. (The chicken will not be completely cooked through at this point.)
Set the cutlets aside on a plate to collect any accumulated juices.
Remove oil from the pan and return to medium heat.
Add the stock, wine, zest and juice and increase the heat to high and cook for about 2 minutes.
Add the chicken back to the sauce, and simmer for another 3 minutes. Pierce the chicken with a small, sharp knife. If juices are clear, the chicken is ready, if still pink, cook another couple minutes until juices are clear.
Add the capers and heat for 1 minutes.
Remove from the heat and gently stir in the butter around the chicken until melted and slightly thickened.
Taste and add a pinch of salt, if necessary.
Serve on warmed platter, or individual plates, and garnish with chopped parsley.