Pre-heat the oven to 350 degrees F.
Place the chicken breasts flat in between 2 pieces of plastic wrap (one piece of plasic below the chicken and one on top). Using a meat tenderizer mallot, lightly pound the thicker ends of the breasts until uniform in thickness.
Salt and pepper the chicken breasts. Spread the flour in a shallow dish and dredge the chicken breasts through the flour on both sides.
Heat 2 tbsp of vegetable oil in a skillet over medium-high heat. Lay the chicken breasts flat in the skillet and cook on each side until golden brown, about 5 minutes per side. Transfer the chicken to a baking sheet and finish in the oven until an internal temperature of 165 degrees F, which is about 15-20 more minutes.
Toss the chopped onion into the skillet and cook until begining to become translucent, around 2 minutes. Add the minced garlic and cook for 30 seconds, stirring frequently. Deglaze the pan with 1/4 cup of white wine, scraping up any brown bits stuck to the pan with a wooden spoon.
Stir in the chicken broth and lemon slices, and bring it all to a simmer. Simmer until it is reduced by 1/2 and is slightly syrupy, about 12 minutes.
While the sauce is simmering, fry the capers. Heat 2 tbsp of vegetable oil in a small skillet until hot, then pour in the drained capers. Fry, stiring frequetly until begining to turn light brown, about 3 minutes. Drain and set aside.
Once the sauce has reduced, pour in the lemon juice and any juices from the cooked chicken. Turn the heat to low and add the butter. Stir until melted.
Remove from the heat and pour over the chicken. Sprinkle with fried capers and parsley and serve over homemade spaghetti, mashed potatoes or any other base you choose! Enjoy!