Bring a large pot of water to a boil. Add ½ teaspoon of salt to the water, then add the egg noodles. Cook for about 8 minutes, stirring occasionally, until tender. Turn off the heat, drain the noodles, and rinse them with cold water to stop the cooking. Set aside.

Using medium heat, bring a large pan or skillet to temperature. Add the butter and let it melt completely. Add the sliced mushrooms and sauté for about 5 minutes, until they begin to soften and release their juices.

Sprinkle the flour evenly over the mushrooms. Stir constantly and cook until the flour has browned slightly and no raw flour remains.

Slowly pour in the chicken broth while stirring. Continue mixing until the broth and roux are fully combined and smooth.

Pour in the half and half. Stir continuously until the mixture is smooth and begins to thicken into a creamy sauce.

Add the shredded rotisserie chicken and the drained pimentos to the pan. Stir to combine evenly. Season with the remaining 1½ teaspoons of salt, the garlic powder, and the black pepper.

Add the frozen peas and stir until everything is well combined.

Allow the mixture to cook for an additional 3 minutes over medium heat, just until the peas are heated through and the sauce is hot and creamy.