Seasoning advice for seitan to replicate gyro meat
Bury it in bread. A meat-substitute burger or kebab meat that has obvious textural or flavor flaws when served bare will often appear near perfect in a pita or bun. Also, you can keep a lot of oil/sauce on it that way, which carries seasonings and juicyness.

Start with baked seitan, made from vital wheat gluten (and 10-20% of another protein flour like lentil or chickpea optimally), and season both in the dough and when sauteing the cut up seitan later - experiment with which seasoning is best added at which time.

Try strong soy sauces (eg chinese light), cumin, smoked salt and/or smoked paprika, sugar, nutritional yeast/msg, flavorful chile pepper powders (eg turkish chile flakes - not just cayenne pepper powder!), garlic, onion. Also add something acidic, eg sumach or lemon.