Preheat oven to 375°F and grease a 9x13-inch baking dish.
Season both sides of your butterflied chicken breasts with salt, pepper, and garlic powder.
Arrange chicken in the prepared baking dish.
Spread a layer of sour cream evenly over the top of each piece.
(Optional but recommended) Add a tiny shake of Worcestershire sauce over each sour cream layer for extra French onion flavor.
Top each piece with a slice or two of provolone cheese (about 8 total for full coverage).
In a small bowl, crush the French-fried onions slightly, then toss them with 4 tbsp melted butter and 2 tsp Worcestershire sauce until coated.
Sprinkle the onion mixture evenly over the chicken.
Bake uncovered for 25–30 minutes, or until the chicken is fully cooked (165°F internal temp) and the topping is golden and crisp.
Rest for 5 minutes before serving to let the creamy sauce settle.