Cut the chicken into thin strips and season generously with salt and pepper. Allow to rest for about 10 minutes.

In a large 12-inch skillet, melt 2 tablespoons of butter over medium-high heat. Add the seasoned chicken strips in a single layer and cook for about 8 minutes, turning occasionally until golden brown and cooked through (internal temperature 165°F). Remove chicken from skillet and set aside.

Add another tablespoon of butter to the same skillet. Toss in the diced onion and minced garlic. Saute for about 5 minutes over medium heat until the onions become translucent and fragrant.

Pour in 1/2 cup of chicken stock and add the sliced roasted red peppers. Bring to a simmer over medium heat, letting it reduce by half (to about 1/4 cup) for about 5 minutes.

Turn off the heat and whisk in 1 cup of heavy cream and 1/2 cup of shredded Parmesan cheese until smooth and well-combined. Return the skillet to medium heat (not medium-high).

Stir in 1 tablespoon of Italian seasoning and the drained 1/2 cup of pepperoncini peppers. Gently fold the reserved chicken back into the skillet. Simmer for an additional 3-5 minutes until everything is heated through and sauce coats the back of a spoon.

Serve over rice, pasta, or steamed vegetables, dividing evenly among 4 plates.