Put 3 tablespoons oil in a wide pan or a deep frying pan and set over medium–high heat.
When hot, add the onion.
Stir and fry for 4–5 minutes or until the onion starts to brown at the edges. Add the ginger and stir for 1 minute. Add the grated tomatoes, salt, cayenne, garam masala and turmeric.
Stir and fry, still on medium–high heat, for 3–4 minutes or until the tomato mixture has thickened a bit.
Now add the carrots and potatoes.
Stir for 1 minute.
Add 120ml (4fl oz) water and stir.
Bring to a simmer.
Cover, turn the heat to low and cook gently for 15–20 minutes or until the potatoes are tender.
Add the peas, stir and cover again.
Cook for a further 4–5 minutes or until the peas are cooked through.
Serve hot.