In order to prepare a Tuna Steak, you will need the following ingredients: lentils, onions, olive oil, garlic, rosemary, parsley, tuna, sage, mushroom, white wine vinegar, sugar, and water.
Heat olive oil in a saucepan. Add onions, garlic, rosemary, and sage. Add lentils, when onions begin to soften. Cover lentils with a water. Simmer on low for 15-20 minutes.
Cook mushrooms in oil in a skillet. Add garlic. Sprinkle on sugar. Deglaze with a bit of white wine vinegar. Cook until most of the liquid evaporates. Add parsley.
Sear the tuna in oil. Remove from pan. Plate it and serve with mushrooms and lentils and a bit of crv®me fraiche.