Fragrant biryani with coriander cod

Name: Fragrant biryani with coriander cod
Ingredients: 2 large onions (320g), halved and sliced; 2 tbsp rapeseed oil; 25g ginger, peeled and cut into thin matchsticks; 1-2 red chillies, deseeded and sliced; 2 tsp vegetable bouillon powder; 250g brown basmati rice; 1½ tsp cumin seeds; ½ tsp ground cinnamon or half a cinnamon stick; 3 cardamom pods, seeds removed and ground; 320g baby spinach; 120g pot plain bio yogurt; 150g frozen peas; 15g coriander, plus extra to serve; 1 tbsp lemon juice; 4 chunky cod loins (560g)