In a spice mill or food processor grind 3 ounces dried porcini mushrooms, large smoked dry chile pepper 1/4 tsp dried wasabi powder. Pulverize to dust. Add tbls of sesame seeds and a pinch of sea salt and a couple of grunds of fresh black pepper. Mix thoroughly in a shallow flat-bottem bowl or plate.
Slice fresh ahi across the grain into about 1.5 inch wide strips. You should have long pieces which are 1.5-inch on each side. Press tuna lightly into rub mixture coating evenly on all sides. Heat cast iron pan on medium high heat. Spray with light coating of non-stick coating. Sear tuna on each of four sides for about 1 minute each.
Cut tuna across into 3 or 4 pieces and serve over wasabi mash potatoes or seasoned rice.
