Heat the olive oil in a lidded casserole or tagine and cook the onion until softened. Add the garlic, aubergines, courgettes and peppers in that order, cooking each for a minute before adding the next.
Add the lemon, cumin and turmeric and stir through to coat the ingredients.
Stir the saffron into the fish stock and pour over the vegetables. Place the fish fillets in the pan on top of the vegetables then add the tomatoes.
Season then place on the lid, turn the heat down and leave to simmer for around 10 minutes or until the fish is just cooked through. Sprinkle over the coriander and serve.