Put the chopped fillet in a bowl. Add vegetable oil, soy sauce, salt and spices. Stir. Cover with cling film and leave to marinate at room temperature for at least 30 minutes. I leave usually on 1 hour.
Deverticalized onion slice not too thinly.
Wash the Apple, remove the seeds, cut into slices.
On a mixture of butter and vegetable oils fry until transparent onion.
Add the marinated meat.
Fry for 5 minutes on high heat, stirring, until lightly browned meat.
Then add the Apple. Reduce the heat, cover and simmer for 10 minutes.