Chop carrots. Mushrooms are just halved. In a skillet over medium high heat, heat oil;saute onion about 3 minutes until soft. Add mushrooms and garlic continue cooking another 5 minutes. Spoon into slow cooker. Add broccoli, carrots, tomato paste and stock. Cover and cook on medium for 4 hours until most of the liquid is absorbed. Caution the carrots may have to be precooked. Cook noodles per directions. In a small sauce pan stir together cornstarch, yogurt and sour cream. Heat gently over low heat for 1 minute. (do not let sauce boilit will curdle) Stir sauce into vegetable mixture. Serve over cooked noodles.