Preheat the oven to 220°C/200°C fan. Boil the potatoes in salted water until tender, drain, then return to the pot to steam dry.
Heat oil in a non-stick ovenproof frying pan (approx. 24cm). Add the cumin, mustard and coriander seeds and stir until aromatic and the mustard seeds are popping. Add the onion and cook for 5 minutes, before adding the turmeric, chilli powder and flakes, and the ginger and garlic. Season with salt and cook everything for several minutes. Add the tomatoes to the pan and coat well, followed by the potatoes and chopped coriander. Stir to coat everything thoroughly and cook for a couple more minutes.
Add beaten eggs. Cook over a low heat until the frittata is mostly set (about 5 mins, by which point the edges will have come away from the pan but the centre will still be liquid), then transfer to the oven until cooked through (7-10 minutes).
Serve in wedges with generous spoons of raita/chutney and reserved coriander leaves.
400g smooth potatoes (such as Desiree), cut into 2cm cubes
1tbsp groundnut oil
1tsp each of cumin seeds, mustard seeds, coriander seeds
1 small onion, finely sliced
1 tsp turmeric
¼tsp each of chilli powder and chilli flakes
2 garlic cloves, finely chopped
2cm piece ginger, finely chopped
2 tomatoes, sliced into 8 wedges each
½ small bunch fresh coriander (10g), stalks and leaves finely chopped, some leaves reserved for serving)
6 eggs, lightly beaten and seasoned
For the raita
½ cucumber grated and wrapped in kitchen towel to dry
handful mint leaves, chopped
For the tomato chutney
1 handful cherry tomatoes
1 small red onion
2tsp onion seeds