Spicy squash and feta frittata

Name: Spicy squash and feta frittata
Ingredients: 2 onions, thinly sliced; 680g/1lb 8oz butternut squash, peeled, very thinly sliced; 2 garlic cloves, grated; 5cm/2in fresh root ginger, peeled and finely grated; 1 tsp ground cumin; 2 tsp smoked paprika; ½ tsp ground chilli; 1 tbsp olive oil; ½ tsp sea salt flakes; 8 free-range eggs, beaten; 160g/5¾oz feta, crumbled; freshly ground black pepper; 25g/1oz fresh mint leaves; ½ green chilli, roughly chopped; 1 lime, juice and finely grated zest; 4 tbsp low-fat plain yoghurt