Charred spring onion chilli feta flatbreads

Name: Charred spring onion, chilli & feta flatbreads
Ingredients: 2 bunches of spring onions (about 250g), trimmed; 3½ tbsp olive oil; 4 garlic cloves, sliced; 1 red chilli (deseeded if you prefer less heat), sliced; ½ tbsp nigella seeds; 100g Greek-style yogurt; 200g feta (vegetarian, if needed), crumbled; 7g sachet fast-action dried yeast; 400g strong white bread flour, plus extra for dusting; 1 tsp caster sugar; 2 tbsp olive oil, plus extra for rising