In the meantime, chop up the rocket and place in a bowl with the tomatoes, mushrooms, olives and spring onions. Prepare a dressing from vinegar, oil and mustard and season with salt and pepper.
When the millet is done cooked, add it to the remaining ingredients in the bowl, spread the dressing over it and mix the salad well.
It tastes lukewarm, but even better if it has been allowed to steep for a while.