In a large frying pan, heat oil over medium heat until hot but not smoking. Add onion and garlic and fry, stirring constantly, for 5minutes. Stir in mushrooms, cpsicum and stock. Cook, stirring occasionally, until vegies are tender and liquid has evapourated, about 6-8 minutes.
Cook noodles according to pack directions, but do not add any salt.
Add chicken, tomato paste, sour cream, nutmeg and black pepper to mixture in the frying pan. Cook, stirring frequently, until heated through, about 2 minutes.
Drain noodles in a colander and divide among bowls. Spoon chicken mixture over noodles. Serve immediately.