Heat the oil in a large saucepan over a medium heat and cook the onion for 5-7 mins until beginning to soften. Mix in the garlic, potatoes, carrots, peppers, leeks and tomato purée, and cook for 3-5 mins more. Pour in the stock and stir in the bay leaf. Bring to a simmer, then cover and cook for 15 mins until the veg is almost tender.

Finely chop most of the dill, reserving a few whole sprigs. Cut the fish into bite-sized pieces and season with salt, pepper and a bit of the lemon juice. Add the fish to the soup along with a pinch of the lemon zest and the chopped dill. Simmer gently over a low heat for 5-7 mins until the fish is cooked through. Remove the bay leaf and season the soup to taste, adding more lemon juice or zest, if needed. Scatter over the reserved dill sprigs to serve.