Thinly slice the onion with a sharp knife or mandoline. Combine 1 tsp sugar and 2 tsp white wine vinegar in a bowl and stir in the onion. Set aside to pickle, tossing occasionally, until needed. Finely chop the tomato. Pick the parsley leaves, discarding the stems.
Step 2 — Make sumac yoghurt
Combine the yoghurt, sumac and 2 tsp water in a bowl. Season with salt and pepper.
Step 3 — Cook lamb mixture
Heat a drizzle of olive oil in a large frypan over high heat. Cook the lamb mince, breaking up the lumps with a spoon, for 3-4 mins until browned. Reduce the heat to medium-high, add the Turkish seasoning and 2 tbs water and bring to a simmer. Cook, stirring, for 1-2 mins until slightly reduced.
Step 4 — Wilt spinach
Add the spinach to the lamb mixture and cook, stirring, for 30 secs or until wilted. Remove from the heat.
Step 5 — Warm tortillas
Put the tortillas on a plate, slightly overlapping, and microwave for 30 secs or until warmed through.
Step 6 — Get ready to serve
ADD FETA OPTION Divide the tortillas, lamb mixture, tomato, drained pickled onion and crumbled feta among plates. Drizzle over the sumac yoghurt and scatter with the parsley leaves to serve.