Take a bowl of cold water and add the salt into it. Stir it and add the onion and radish slices. This will prevent the radish from discoloring and take away most of the sharpness. Let to soak until you are done with the steak.
Use a kitchen paper to pat the steak dry. Rub olive oil, herbs and ground pepper on both sides of it. Cook it in the pan for 3 minutes on each side, depending on how cooked do you like it. Remove from the heat and let it cool down on an open dish until you prepare the dressing.
Make the dressing now in a small bowl. Whisk the remaining olive oil, the walnut oil and vinegar together. Slice up the steak now.
Put the onions and radishes into another large bowl after draining off their water. Add the dressing, steak slices and celery to the bowl. Toss together well to combine everything.
Divide the salad leaves among the individual salad platters. Use a spoon to scoop the salad unto the leaves. Serve right away.