Preheat oven to 350°F.

Bring a large pot of water to a boil. Add the egg noodles and cook according to package directions. Drain and set aside.

While the noodles are cooking, dice the onion and garlic.

Heat the butter in a small skillet over medium heat. Cook the onion until softened, about 5 minutes. Add the garlic and cook an additional minute.

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

Stir the cooked egg noodles into the creamed mixture and stir to coat.

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