Preheat oven to 350 degrees.

Cook according to package directions, drain and set aside.

While the noodles are cooking, heat the butter in a small skillet over medium heat. Add in the onion until softened, about 5 minutes. Add the garlic and cook an additional minute just until fragrant.

In a large bowl, combine the onion and garlic with the chicken, soup, sour cream, peas and carrots, mustard, salt, and pepper. Stir to combine.

Add in the cooked egg noodles and stir to coat.

Spoon into a 9x13 baking dish. Bake at 350 degrees for 15 minutes or until heated through.