In a small sauce pot, whisk together soy sauce, sugar and water.
Heat the mixture over high heat, bring to a boil, then set aside.
In a separate small sauce pot, heat the wine over high heat until reduced to 1/4 cup.
Add the reduced wine and miso to the soy mixture and stir to combine well.
Let the mixture cool, then pour over the beef tenderloin in a resalable plastic bag.
Refrigerate overnight.
Pull the Beef Tenderloin out of the marinade and let come to room temperature.
Preheat the Big Green Egg to 650°.
Sear the tenderloin for 2 minutes each side directly over the coals (bottom tier).
Now pull the tenderloin off and bring the temp of the BGE down to 400°.
Put the tenderloin on the top tier or raised grid and cook for another 20 - 30 minutes flipping occasionally until the meat measures 130° for medium rare.
Pull the tenderloin and let rest for 10 minutes.
Slice and serve over Panzanella.