Preheat your oven to 350°F.

Butterfly 2–3 large boneless, skinless chicken breasts all the way through to create 4–6 thinner pieces of chicken.

Add ½ of a large red onion, sliced into half-moon rounds, to the bottom of a 9×13-inch baking dish.

Drizzle the onions with 1 tablespoon of olive oil and sprinkle about ¼ of the Hidden Valley Ranch seasoning packet over the top. Toss the onions directly in the baking dish, then spread them into an even layer.

Arrange the butterflied chicken pieces in a single layer over the seasoned onions.

Sprinkle the remaining ranch seasoning packet evenly over all the chicken.

Spoon about ¼ cup of barbecue sauce over each whole chicken breast, dividing it evenly between the butterflied pieces.

Add 3–4 sliced pepperoncini to each piece of chicken, then drizzle about 1 teaspoon of pepperoncini juice over the entire baking dish.

Sprinkle 2 cups of freshly shredded mozzarella evenly over the chicken.

Add 1½ cups of French fried onions to a large zip-Lock bag. Gently crush them with your hands, keeping the pieces rustic and chunky rather than crushing them into fine crumbs.

Pour in 4 tablespoons of melted salted butter. Seal the bag and shake everything together until the onions are evenly coated.

Sprinkle the buttery French fried onions evenly over the mozzarella.

Cover the baking dish very tightly with aluminum foil, crimping it securely around all four sides of the dish.

Bake covered at 350°F for 25 minutes.

Carefully remove the aluminum foil and return the baking dish to the oven uncovered.

Bake for another 10–15 minutes, or until the chicken is cooked through, everything is piping hot and bubbling, and the French fried onion topping is golden brown.

Let the chicken rest for about 5 minutes before serving.