Rinse the meat and pat dry. Slice in 0.5 inch thick pieces.
Place one piece of meat in the marinade bowl and rub it with your fingers. Repeat for all the slices.
Slightly grease a pan with cooking spray.
Place the beef in the skillet and cook for 2-3 minutes on each side.
When you flip over, add the remaining marinade in the cooking skillet, coating the beef.
When the meat is ready, remove from the pan and set aside.
Cut the potatoes in very thin slices.
Heat the vegetable oil in the pan and add the potatoes.
Sprinkle with salt and pepper and add the rosemary leaves.
Cook until they get golden on one side and then flip over.
Serve with the lemony beef.