Leave to marinate the tuna in fresh rosemary for a couple of hours (I leave it 12 hours more flavorful)
In a skillet member
saute the mushrooms that you previously cut.
Also add the spinach with the mushrooms, and water spinach, is seeking a compoto both with the addition of salt and pepper
After putting the mushrooms and spinach, hot (in oven) roasting the tuna with rosemary (I like medium rare)
At the end of this and the result as you can see from the pictures (FotoMaskaGrafia), can also be creative and add a touch of whimsy to the plate as I did.
Do not forget that tuna can be served with red wine (light wine to keep in the fridge)