Begin by slicing each chicken breast horizontally into 2 or 3 thinner portions. If needed, gently flatten the pieces using a meat mallet until they reach a uniform thickness of approximately ½ inch.
Generously season both sides of the chicken slices with the Italian herb blend, salt, and pepper. Using a pastry brush, lightly coat one side of each piece with the melted butter, ensuring the butter is not too hot to avoid cooking the meat prematurely.
Warm the olive oil in a spacious skillet over medium-high heat. Once heated, sear the chicken in batches, cooking each side for roughly 4 to 5 minutes until a golden crust forms. Remove the seared chicken from the skillet and set aside.
In the same skillet, lower the heat to medium and combine the cream of chicken soup, milk, sour cream, Ranch seasoning mix, and onion powder. Stir the mixture continuously until smooth and cohesive.
Allow the sauce to come to a gentle simmer. Let it reduce slightly for 5 minutes, stirring occasionally. Once the sauce thickens slightly, return the cooked chicken to the skillet and spoon some sauce over each piece.
Partially cover the skillet and allow the chicken to finish cooking and soak up the sauce's flavor, approximately 10 minutes more.