Season the chicken strips generously with salt and black pepper.
In a large skillet or sauté pan, heat the olive oil over medium-high heat. Sear the chicken in batches until golden brown on both sides, approximately 3 minutes per side. Remove chicken from the pan and set aside.
Reduce heat to medium and add the butter to the same skillet. Once melted, add the onions and mushrooms. Sauté until the mushrooms are browned and the onions are translucent, about 7-8 minutes.
Add the minced garlic and cook for 60 seconds until fragrant.
Sprinkle the flour over the vegetables and stir constantly for 1-2 minutes to cook out the raw flour taste.
Slowly whisk in the chicken broth, scraping the bottom of the pan to release the fond. Stir in the Dijon mustard and smoked paprika.
Simmer the sauce for 3-5 minutes until it begins to thicken.
Return the chicken and any accumulated juices to the skillet. Simmer for an additional 2 minutes until the chicken is cooked through.
Reduce the heat to low. Stir in the sour cream until completely incorporated and the sauce is smooth. Do not allow the sauce to reach a boil once the sour cream is added to prevent curdling.
Adjust seasoning with salt and pepper. Serve the chicken and sauce over warm egg noodles and garnish with chopped parsley.