Heat a small, dry frying pan, toss in the coriander and cumin seeds and toast for a few minutes, shaking the pan often, until they start to smell fragrant. Remove from the heat and grind the seeds to a powder using a pestle and mortar. Stir in the oil and a pinch of salt.
Tip the mango cubes into a serving bowl with the salad onions. Pour the lime juice over along with the spiced oil, then gently stir together with the chopped coriander. Taste and add a little more lime juice if you wish, then serve scattered with extra chopped coriander.
Goes well with mini poppadums as an appetizer, or served with chicken.
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