Slice the polenta 1 centimetre thick. Cut each slice into 4 little wedges.
Heat a wide nonstick skillet. Add a drop of the oil and spread it around with a paper towel to create a very light coat, or use cooking oil spray. Add the polenta wedges; cook in a single layer over medium heat, about 5 minutes on each side.
Remove the polenta to a plate. Heat the oil and soy sauce slowly in the same skillet. Before they get too hot, add the seitan and stir well. Raise the heat to medium-high and sauté, stirring frequently, for 5 minutes. Stir in the bok choy, spinach and scallions, then cover and cook until just wilted, 1 to 2 minutes.
Sprinkle in vinegar to taste. Gently fold in the polenta wedges and dried tomatoes. Season with salt and pepper and serve at once.