Wash the rosemary, pluck a few needles and chop them. Mix with 1 teaspoon of oil and some pepper. Dab medallions and coat with rosemary oil. Chill for about 30 minutes.
Wash the peppers and cut them into large cubes. Cut onion into fine slices. Wash and dice potatoes.
Heat 1-2 teaspoons of oil in a coated frying pan. Fry the potatoes for 15-20 minutes at medium heat until golden brown. Season with salt and pepper.
Heat a second pan. Fry the medallions for about 3 minutes on each side. Salt them, take them out and keep them warm. Fry the bell pepper, onion and remaining rosemary twig in hot fat while turning for about 5 minutes.
Season with salt, pepper and lemon juice. Heat the meat again briefly. Arrange the meat, peppers and potatoes on a plate. Garnish with rosemary.