Thinly slice the red bell pepper and dice the yellow onion.

Thinly slice the pepperoncini peppers into rings or measure out 1/2 cup of sliced pepperoncini.

Finely grate the Parmesan cheese or measure 1/3 cup store-bought grated.

Cut the chicken breasts across the grain into 1/2-inch-thick slices. Place in a large bowl, add 3/4 teaspoon of kosher salt and 1/4 teaspoon black pepper, and toss to coat.

Heat 2 tablespoons of 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 and cooked through, about 6 minutes total. Using tongs, transfer to a plate. Repeat with the remaining chicken.

Add the remaining 1 tablespoon of olive oil to the skillet. Add the bell pepper, onion, remaining 1/2 teaspoon kosher salt, and Italian seasoning. Cook until beginning to brown, about 2 minutes.

Add the chicken broth and scrape up the browned bits from the bottom of the pan. Cook until the broth is reduced by half, about 2 minutes.

Add the Parmesan and heavy cream. Bring to a simmer and cook until slightly thickened and the peppers are tender, about 3 minutes.

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.