Preheat your oven to 200°C and line a large baking tray with parchment paper.
Dice the potatoes into 1cm cubes, toss them with 10ml of olive oil and a pinch of sea salt, then roast for 25 minutes until golden and crispy.
Slice the seitan into thin strips and toss in a bowl with the oregano, garlic powder, onion powder, smoked paprika, salt, and pepper.
Grate 50g of the cucumber, squeeze out all excess moisture using a kitchen towel, and stir it into the Greek yogurt along with minced garlic and lemon juice to make the tzatziki.
Chop the remaining cucumber, cherry tomatoes, and red onion into bite-sized pieces; crumble the feta cheese and set aside for the salad.
Heat the remaining 10ml of olive oil in a non-stick pan over medium-high heat and sear the seitan strips for 5-7 minutes until browned and crispy on the edges.
Assemble the bowls by dividing the roasted potatoes and seitan gyros, then add the fresh Greek salad, olives, and a generous dollop of creamy tzatziki.