Thinly slice the red bell pepper and dice the yellow onion. Slice the pepperoncini peppers into rings or measure out sliced pepperoncini. Grate the Parmesan cheese.

Cut the chicken breasts across the grain into ½-inch-thick slices. In a bowl, add the chicken, ¾ teaspoon kosher salt, and ¼ teaspoon black pepper and toss.

Heat 2 tablespoons of olive oil in a skillet over medium-high heat. Cook half the chicken until browned (about 6 minutes), then transfer to a plate. Repeat with remaining chicken.

Add the remaining olive oil to the skillet. Add bell pepper, onion, remaining salt, and Italian seasoning. Cook until beginning to brown, then add chicken broth and reduce by half.

Stir in Parmesan and heavy cream, bringing to a simmer until thickened. Return chicken and juices to pan, add pepperoncini and toss. Serve with more Parmesan if desired.