Harissa sweet potatoes with roasted garlic & tahini dressing

Name: Harissa sweet potatoes with roasted garlic & tahini dressing
Cuisine: African
Ingredients: 1kg sweet potatoes, skin on and cut into chunks; 3 tbsp harissa paste; 1 head of garlic; 3 tbsp plain coconut yoghurt; 2 tbsp runny tahini; 1 tbsp juice of a lemon; 1/2 tbsp extra virgin olive oil; 1 tsp maple syrup; Salt; Pepper; 2 spring onions, finely sliced; 5g chopped fresh coriander; A pinch of chilli flakes