Boil a large pan of salted water. Add the potatoes and cook until just tender – 12-15 minutes.
Meanwhile, toast all the seeds in a hot dry frying pan for 2 minutes until fragrant. Crush them in a pestle and mortar, then set aside.
Drain the potatoes and steam dry in the colander for a minute.
Heat the grill to high. Put the potatoes on a baking tray. Brush with oil and grill until crispy and browned – 5-7 minutes. Turn the potatoes over and repeat to crisp and colour the other side.
Put the crushed spices in a large bowl with the melted butter, spring onions, coriander and chillies.
Remove the potatoes from the grill and divide each one in half, using a metal spoon so you create rough edges. Put the potatoes straight into the spice bowl and toss until well combined.
Add the sea salt, lime juice and kebab masala, adjusting them to taste, then serve.