"For those who have experienced the omnivore version of a gyro, the taste cannot be forgotten. For those vegans who never have, but want something really awesome in a pita bread with hot food, cold veggies, and tangy yogurt sauce, this is what you are looking for! You can eat these sandwiches open-faced, or fold them in half (like a taco) to enjoy the way they were meant to be eaten."
Grate cucumber into a colander; place in a sink and allow to drain for 20 minutes. Squeeze out remaining moisture and transfer to a small bowl. Add vegan yogurt, lemon juice, dill, chives, sucanat, salt, and black pepper and stir well. Cover and refrigerate until needed. Stir well before using.
Heat olive oil in a saute pan over medium heat. Add garlic and cook gently until golden, about 1 minute. Add seitan in a single layer, if possible. Brown seitan gently, about 5 minutes. While seitan cooks, blend cumin, oregano, basil, cinnamon, nutmeg, and chili powder together in a bowl. Sprinkle spice mix over browned seitan and toss. Continue browning seitan until heated thoroughly and golden brown, about 5 minutes more.
Assemble a sandwich by layering seitan, tomato, onion, and lettuce on a pita. Spoon sauce on top. Repeat with remaining fillings, sauce, and pita.