Heat the oil in a large, heavy-based saucepan over a medium heat, add the onion and cook for 5 minutes or until beginning to soften. Add the garlic, squash, carrots and spices and fry gently for a further 5 minutes.
Stir in the tomato purée, then pour in the stock and season with salt and pepper to taste. Cover and simmer gently for 20–25 minutes or until the vegetables are tender. Stir in the mango and simmer gently for a further 5 minutes.
Ladle the tagine into serving bowls and sprinkle with the coriander and serve with steamed couscous.