Preheat oven to 200C/400F/Gas 6.
Place a large saucepan over low heat and spray with cooking spray. Add the onions, carrots, garlic, ginger, and a splash of water, and cook for about 10 minutes, or until the vegetables are soft. You may need to add more water.
Turn heat to high, add the beef mince and cook until browned.
Stir in the turmeric, ground coriander, ground cumin, and chili powder, then add the canned tomatoes, tomato purée, and hot beef stock. Stir to combine then season to taste with salt and pepper.
Reduce heat to simmer for about 30 minutes, or until the liquid has reduced and the mixture has thickened. Stir the peas into the mince.
Meanwhile, make the Bombay potato topping by boiling the potatoes for 2-3 minutes until just tender. Drain then transfer to a large bowl. Add the cumin seeds, ground cumin, turmeric, and chili powder. Gently mix together and season to taste with salt and pepper. Don't worry if the potatoes break up!
Transfer the beef mixture to a large ovenproof dish.
Spoon the potatoes over the top and spray with low-calorie cooking spray.
Bake for 30-40 minutes or until hot throughout and the potatoes are golden brown.