1. Pound breasts until 1/4 thick.
2. Dredge in flour mixture.
3. Heat oil over medium heat.
4. Add chicken and saute about 7 minutes, turning once.
5. Remove and keep warm.
6. Add butter to frypan and increase heat to high.
7. Add onion and mushrooms.
8. Saute about 5 minutes.
9. Reduce heat to low.
10. Add cream, parsley, mustard and lemon juice.
11. Bring to a boil stirring constantly.
12. Add juices from chicken into cream mixture.
13. Pour sauce over chicken and serve.