In a large skillet set over medium-high heat, add 1 tablespoon of olive oil.
Meanwhile, place the cut chicken into a bowl. Season with garlic powder, onion powder, paprika, cayenne pepper, and ½ teaspoon each of salt and pepper; toss to combine.
Add the chicken in a single layer, working in batches if needed. Cook until deeply golden on the outside, then transfer to a plate. The chicken does not need to be cooked through at this point. Let them develop a deep golden sear before turning. Remove from the pan and transfer to a plate.
Add the remaining 1 tablespoon olive oil and mushrooms. Cook until the mushrooms release their liquid, the liquid cooks off, and they begin to brown. Add the onion and cook until softened, then stir in the garlic and cook until fragrant. Scrape up any browned bits from the bottom of the skillet as the vegetables cook.
Add butter and all-purpose flour and cook, whisking constantly, for about 1 minute. SLOWLY add 2 cups chicken broth, whisking to create a smooth sauce. Add 1 tablespoon Dijon mustard, if using, 1 tablespoon Worcestershire sauce, ½ teaspoon fresh thyme, and the remaining salt and pepper. Simmer until the sauce is smooth and thick enough to coat the back of a spoon.
Toss in the chicken, turn the heat down to medium-low. Continue to cook for 5-8 minutes or simmer until the chicken reaches 165°F in the center. Add the egg noodles and stir until combined. Cook for 2 more minutes.
Add salt and pepper to taste. Remove the skillet from the heat, then stir in the sour cream until smooth and garnish with fresh parsley, if desired.