Roughly chop seitan into bite-sized chunks. Set aside
Heat olive oil over medium heat in a large pan. Add onions and cook until translucent, about 3 minutes. Add garlic and cook, stirring, for an additional minute
Add spices to pan and stir to combine. Cook additional 2-3 minutes, until fragrant
Add tomato paste, and stir to combine
Add in seitan, soy sauce, maple syrup, and apple cider vinegar. Lower heat to simmer and cook, stirring occasionally, 10-15 minutes
Transfer mixture to an airtight container and allow to marinate overnight
Tzatziki:
Grate cucumber with skin on. Transfer to a fine-mesh strainer and squeeze out extra moisture
Add Vegenaise to large mixing bowl, add cucumber and remaining ingredients. Stir to combine
Taste and adjust seasonings
Gyros:
Warm pitas up in an oven and transfer to a cutting board.
Spread a thin layer of Tzatziki on each pita, then evenly distribute lettuce, cucumber, tomato, seitan, Feta Crumbles, and parsley.
Fold pitas over and wrap in parchment paper. Enjoy!