Persian pea and potato stew

Ingredients

• 90ml olive oil, plus extra to serve
• 2 onions, finely chopped (250g)
• 2 tsp cumin seeds
• 15g ginger, peeled and finely chopped
• 1 lemon, zest thinly shaved to get 6 strips, 1 tbsp juice
• ½ tsp ground turmeric
• 5 garlic cloves, crushed
• 960g frozen petits pois
• 2 large maris piper potatoes, peeled and cut into 1cm chunks (340g)
• 500ml vegetable stock
• 10g coriander leaves (or mint), finely chopped
• 80g plain yoghurt, to serve
• Fine sea salt and black pepper