Heat the olive oil in a large frying pan over medium heat.
Season the chicken and cook until lightly golden. Remove and set aside.
Cook the onion until soft, then add the garlic and mushrooms. Cook until the mushrooms become tender.
Stir in the flour and paprika, cooking for 1 minute.
Gradually add the chicken stock, then stir in the tomato purée.
Return the chicken to the pan and simmer for about 10 minutes.
Lower the heat and stir in the sour cream and Dijon mustard without boiling.
Garnish with fresh parsley and serve with cooked rice or pasta.