Pat the chicken breast pieces dry, and sprinkle them with salt and pepper.
Heat the oil and butter in a large sauté pan over medium high heat.
Saute the chicken breasts until golden on each side (about 2 minutes per side)
Remove the chicken from the pan, and place on a plate, and set aside.
Add the onions, mushrooms and garlic to the saute pan, and let cook for about 2 more minutes until softened.
Add the flour, and stir for about 30 seconds. Add the tomato paste, and stir again to combine.
Slowly pour in the Progresso Cooking Stock, salt, and tarragon, and stir well. Bring the stock to a boil, and then add the dried pasta. Mix to submerge the pasta, and lay the chicken breasts on top of the pasta.
Reduce the heat to low, cover, and let simmer for about 8-10 minutes or until the chicken is cooked through, and the pasta is al dente.
Remove the pan from the heat.
Place the Greek yogurt in a bowl or measuring cup, temper the yogurt by slowly adding a soup ladle full of the pan sauce to the yogurt, while stirring to combine.
Add the warmed yogurt into the sauce, and stir well to combine the chicken and noodles with the sauce.