Wash the lamb fillets and pat them dry. Heat olive oil in a pan and fry the lamb fillet in it all around at medium heat for 10-12 minutes. Season with salt and pepper. Leave to cool.
Squeeze 1 orange. Peel the garlic clove and cut into fine slices. Pluck rosemary needles from the stem. Chop the walnuts coarsely. Heat 1 tablespoon of walnut oil in a pan and fry the garlic and rosemary.
Add the walnuts and roast briefly. Deglaze with orange juice and season with salt, pepper and sugar. Let it cool down and beat the remaining walnut oil into it. Clean, wash and drain the salad.
Cut romaine lettuce into strips. Clean, wash and quarter the tomatoes. Peel the remaining orange so that the white skin is completely removed. Cut the orange into slices and put them together with
Cut the lamb fillets into slices and arrange on the salad. Spread orange-nut marinade on top. Serve garnished with orange slices as desired.