Half-fill a saucepan with cold water and add the potatoes and carrots. Bring to the boil and cook for 8 minutes. Add the cauliflower florets and cook for 2 minutes more. Drain in a colander and set aside.
Heat the oil in a large, non-stick frying pan or wide-based saucepan. Add the onion and cook over a medium heat for 8 minutes or until well softened and lightly browned, stirring regularly. Sprinkle over the curry powder and cook for 30 seconds more, stirring.
Add the tomatoes to the onions and cook for 2–3 minutes, stirring constantly. Add the stock and bring to a gentle simmer. Add the vegetables and peas or spinach and simmer gently for 5 minutes, stirring regularly. If the sauce thickens too much, add a splash of water.
Serve immediately with yoghurt and mango chutney.