Preheat the oven to 230°C fan.
Mix the cauliflower florets (with any young leaves attached) in a large bowl with the onion, oil, 2 teaspoons of curry powder, ¾ teaspoon of salt and plenty of pepper. Once combined, spread out on a large parchment-lined baking tray and roast for 15 minutes, until soft and golden-brown but still retaining a bite. Remove from the oven and set aside to cool.
Fill a medium pan with plenty of water and bring to the boil on a high heat. Reduce the heat to medium-high, then carefully lower in the eggs and boil gently for 10 minutes, until hard-boiled. Drain the eggs, then return them to the same pan filled with running cold water to stop them cooking. Once cool, peel the eggs, place them in a large bowl and break them roughly with the back of a fork to form large chunks.
In a separate small bowl, mix together the yoghurt, mayonnaise, the remaining 1 teaspoon of curry powder, half the Aleppo chilli flakes, the cumin, the lemon juice and ¼ teaspoon of salt. Add the sauce to the eggs, along with the cauliflower and onion and the tarragon. Mix together well, spoon the mixture on to a large plate, then sprinkle over the remaining chilli flakes and serve, along with the lemon wedges.