Thinly slice 1 medium red bell pepper and dice ½ medium yellow onion. Thinly slice 10 whole pepperoncini peppers into rings. Finely grate 1 ounce Parmesan cheese.

Cut 1 ½ pounds boneless, skinless chicken breasts across the grain into ½-inch-thick slices. Place in a large bowl, add ¾ teaspoon of the kosher salt and ¼ teaspoon black pepper, and toss to coat.

Heat 2 tablespoons of the olive oil in a large skillet over medium-high heat until shimmering. Add half of the chicken in a single layer and cook until deeply browned. Transfer to a plate and repeat with the remaining chicken.

Add the remaining 1 tablespoon olive oil to the skillet. Add the bell pepper, onion, remaining kosher salt, and Italian seasoning. Cook until beginning to brown. Add the chicken broth and scrape up the browned bits from the bottom of the pan.

Add the Parmesan and heavy cream. Bring to a simmer and cook until slightly thickened. Return the chicken and any accumulated juices to the pan. Add the pepperoncini and toss to coat in the sauce. Serve with more Parmesan cheese if desired.