Heat 4 tablespoons of olive oil in a large frying pan and cook the tuna steaks. Bake for 3 minutes on one side, turn and cook for the same duration on the other. Sprinkle the slices with half a glass of dry white wine; let it evaporate over high heat, then add salt and pepper, then remove from heat. Coarsely chop pitted olives, pine nuts, a few sprigs of marjoram and garlic (with a knife or in a food processor). Wash the lemon and carefully peel only the yellow part of the zest. Sprinkle tuna steaks with chopped olives, with lemon slices and serve immediately with boiled potato and salad.