For the Marinade: Whisk together tamari, wine, and set aside about half the liquid in a small bowl. Add baking soda and corn starch to the original bowl and whisk to combine. Place seitan chunks in original bowl that now has the baking soda and corn starch added, toss to coat thoroughly. Cover with plastic wrap and set aside while you prepare the other ingredients.
For the Batter: Whisk flour, 1/4 cup corn starch (reserve the remaining 1/4 cup), baking powder, and salt in a large bowl. Add reserved marinade and whisk until mixture is thick and clumpy. Add a little more water if necessary to thin. Set aside.
For the Sauce: Combine tamari, wine, vinegar, water, syrup, sesame oil, and cornstarch in a small bowl and stir with a fork until cornstarch is dissolved and no lumps remain. Set aside.
Place a medium-sized skillet over low-medium heat and add oil. When oil has warmed, add garlic, ginger, minced scallions, and red chili peppers and stir, being careful not to let garlic turn brown. Cook, stirring, until vegetables are aromatic and soft, but not browned, about 3 minutes. Stir sauce mixture (as cornstarch will have settled on the bottom of the bowl) then add to skillet. Cook, stirring, until sauce starts to thicken and bubble, about 1 minute. Add green scallion segments and stir for another minute or two. Transfer sauce to a bowl to stop cooking, but don’t wipe out skillet
To Finish: Heat oil in a large wok or pot to 350°F and adjust flame to maintain temperature. (You want the oil to be about 2 to 3 inches deep.) It’s important to have the right temperature for frying or else the food absorbs too much oil.
Place remaining 1/4 cup of corn starch on a small plate and, working one piece at a time, transfer seitan from marinade to cornstarch, tossing lightly to coat. Transfer pieces to the bowl with batter, and turn over, ensuring that it’s totally covered. Leave seitan in after bowl until ready to fry.
With a fork, lift one piece of seitan at a time out of the coating, letting some of the excess drip off, and carefully lower into hot oil. Once all the seitan is added, cook on one side until golden brown then flip over to cook other side. Once you add the seitan, the temperature of the oil will drop so adjust heat to maintain temperature.
Remove with a metal spider or slotted spoon when all sides are nicely browned and place on a paper towel-lined plate to drain. When all the seitan has been fried, place sauce skillet over medium heat and return the sauce to the skillet, then add seitan pieces. Toss to coat all the pieces in the thickened sauce for a minute or two and remove pan from heat. Alternatively, you can arrange seitan on a platter and drizzle sauce on top. Sprinkle with sesame seeds.