Shawarma-spiced roast lamb leg with beetroot sauce

Name: Shawarma-spiced roast lamb leg with beetroot sauce
Prep time: 40 min
Cook time: 2 h 40 min
Total time: 3 h 20 min
Cuisine: Middle Eastern, African
Ingredients: 6 garlic cloves, peeled; 4 preserved lemon quarters, rinsed, flesh discarded, rind coarsely chopped; 2 tbsp baharat (see note); 1 tbsp Aleppo pepper (see note); 1 tbsp sumac; 70 ml olive oil; 1 lamb leg (about 1.7kg), bone in; Warmed flatbread, to serve; 2 beetroot, stalks trimmed; 200 gm Greek-style yoghurt; 2 tbsp extra-virgin olive oil; 1½ tbsp hulled tahini; Juice of 1 lemon, or to taste; 2 garlic cloves; 1 tsp Aleppo pepper (see note); 2½ tbsp olive oil; 100 ml red wine vinegar; 1 tsp caster sugar; 1 Spanish onion, thinly sliced; 1 cup torn mint; 1 cup torn flat-leaf parsley; 1 cup torn coriander; 2 tbsp extra-virgin olive oil; Juice of ½ lemon