1For Wasabi Glaze: Mix together first 6 ingredients. The slowly incorporate that mixture into the white miso until a glaze is formed. Adjust saltiness with sugar. The flavor should be of a sweet, salty, wasabi.
2For Red Pepper Coulis: Roast peppers until charred. Remove the skin and seeds. Reserve any liquid that comes from the peppers.
3Puree in a blender until smooth. Add the remaining ingredients and puree until all ingredients are incorporated.
4Grill your tuna to your temperature of choice. Serve with the wasabi glaze, on top of the coulis.
There are plenty of uses for roasted red peppers, and though a store-bought jar of them will do in a pinch, freshly roasted and skinned peppers are easy enough to do yourself. This method involves a little more energy than others—a little dinner-prep calisthenics.