Drain the mung beans, place in a saucepan and cover with cold water. Bring to the boil then reduce to a simmer and cook the beans for 30 minutes, until they are soft. Remove from the heat, and drain.

Meanwhile, heat half the olive oil in a large saucepan on a low heat and sauté the onions for 20-25 minutes, until they are soft and lightly golden.

Combine the rest of the olive oil, red wine vinegar, mustard, parsley and shallots in a bowl, and season. Add the warm mung beans and toss in the tomatoes. Finally, top with the cooked onions.

Serve hot or cold, sprinkled with nigella seeds.