Preheat a large skillet, preferably cast iron, over medium-high heat.Dredge half the seitan slices in flour to coat. Add a thin layer of olive oil to the pan, and cook seitan until lightly browned, about two minutes on each side. Coat the other slices and repeat. Place the cooked seitan on a plate and cover with aluminum foil, to keep warm.
Do not rinse out the skillet, as you’re going to make the sauce in it. If there is enough oil left in the seitan the go ahead and saute the onions in it. if not, add a little oil and saute them for about 5 minutes, until lightly browned. Add garlic and saute for a minute or so.
Add the wine and raise the heat to bring to a rolling boil. Add the vegetable broth, salt, black pepper, and thyme. Let boil and reduce for about 7 minutes.
Lower heat, add capers and lemon juice, plus the nutritional yeast to thicken a bit. Cook for another minute or so, to heat the capers through.
Serve over mashed potatoes and greens, with plenty of sauce on top. Garnish with chopped chives.