Place potato into a small saucepan and cover with cold water by at least 3cm. Bring to the boil, add a good pinch of salt and cook for 6-8 minutes or until fork-tender. Drain into a colander and set aside.
Heat oil in a non-stick frying pan over medium heat until hot. Add the cumin seeds and cook, stirring often, for 1-2 minutes or until fragrant. Add the onion, ginger, chilli and a pinch of a salt, cook for 5 minutes or until softened.
Add all the spices, cook 1 minute then add the frozen peas. Cook, stirring, for a further 2-3 minutes or until they turn bright green. Remove the pan from the heat and add the potatoes, stirring to combine. Add the lemon juice, coriander and season to taste with salt and pepper. Set aside to cool completely.