Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Season chicken breasts with salt and pepper, then cook until golden brown on both sides, about 5 minutes per side. Remove and set aside.

In the same skillet, sauté sliced onions and minced garlic for 3 minutes until soft and fragrant. Add the pepperoncini peppers and cook for 2 minutes more.

Pour in the chicken broth, scraping up any browned bits, then stir in the heavy cream and bring to a gentle simmer.

Return the chicken to the skillet, cover partially, and simmer over medium-low heat for about 10 minutes, until cooked through and the sauce thickens.

Taste, adjust seasoning, and finish with freshly chopped parsley before serving.