Cut your turkey breasts into 4 approximately equal pieces. Working with one piece at a time, cover the turkey with a piece of parchment paper or plastic wrap and, using a meat mallet, a heavy bottomed skillet, or a rolling pin, pound the turkey till a scant ½ cm thick. Season with salt and pepper. Add the flour to a shallow dish and toss in the turkey cutlets to coat. Set aside.
Place a large cast iron skillet or heavy bottomed sauté pan over medium heat and add in a splash of oil. Fry the turkey cutlets for 2 to 3 minutes per side, or until golden and cooked through, adding more oil as needed. Transfer the turkey to a plate and set aside while you make the sauce.
Reduce the heat to low and add in 2 tablespoons of the butter along with the onion. Season with salt and pepper and cook down for 1 to 2 minutes or until softened. Whisk in the wine, lemon zest, and lemon juice, and simmer for 2 minutes to reduce slightly. Whisk in the remaining 2 tablespoons of butter along with the capers and parsley.
Add the turkey back into the pan, flipping to coat and serve immediately.
