Heat a large skillet over medium-high. Sprinkle chicken with 1 teaspoon of the salt and ½ teaspoon of the pepper. Add oil to skillet and swirl to coat. Add chicken; cook, stirring occasionally, until browned on all sides and a thermometer inserted in thickest part registers 165°F, about 6 minutes total. Transfer to a large bowl using a slotted spoon, leaving drippings in skillet; set aside.

Add butter to reserved drippings in skillet and increase heat to medium-high. Add mushrooms; cook, stirring occasionally, until starting to brown, about 5 minutes. Stir in onion, green bell pepper, and garlic; cook, stirring occasionally, until vegetables are softened and browned, about 5 minutes.

Add sherry; cook over medium, stirring constantly to scrape up browned bits, until reduced, about 2 minutes. Add flour; cook, stirring constantly, until thickened into a paste, about 1 minute. Slowly pour in chicken broth and heavy cream; cook, stirring constantly, until smooth. Stir in Dijon, and remaining ¼ teaspoon each salt and pepper. Bring to a simmer over medium; reduce heat to medium-low; simmer over medium-low, stirring occasionally, until thickened to a desired consistency, about 2 minutes.

Stir pimientos, peas, chiles, and reserved cooked chicken into sauce over medium-low; remove from heat. Serve over cooked egg noodles and sprinkle with parsley.