Combine spices, garlic, lemon rind and oil in a small bowl, then rub all over lamb in a large ceramic dish, cover with plastic wrap and set aside to marinate for 30 minutes.
Meanwhile, for cauliflower salad, preheat oven to 200ᵒ󠇥C. Toss the cauliflower and 50ml oil in a bowl to coat, season to taste. Spread on baking trays lined with baking paper and roast until tender and golden brown (20-25 minutes). Transfer to a bowl, add chickpeas, preserved lemon and onion, then set aside to cool slightly. Just before serving, add remaining ingredients, season to taste and toss to combine.
For pea tabbouleh, cook quinoa in a saucepan of boiling salted water until tender (12-15 minutes), drain through a fine sieve and rinse under cold running water. Drain well, spread on a tray to dry out (15 minutes), then combine in a bowl with peas, cucumber, herbs and spring onion. Whisk olive oil, vinegar and garlic in a bowl to combine, season to taste and toss through salad just before serving.
Preheat a barbecue or char-grill to a medium – high. Barbecue lamb, fat-side down first and turning every 10 minutes or so, until cooked to your liking (30-35 minutes for medium - rare). Transfer to a tray, cover with foil and rest for 15 minutes, then slice and serve with salads, yoghurt, pita an lemon wedges.