Rinse the quinoa. Bring the water and stock cube to boil in a medium size pot and add the quinoa; cook for about 15 mins or untill fluffy.
Meanwhile, in a large frying pan, heat the remaining olive oil over medium heat. Add the onion and sweat for a minute. Turn the heat up to medium high and add the asparagus along with a pinch of salt. Saute until the asparagus is tender, about 5 to 10 minutes.
During the last couple of minutes, add the lemon zest to the asparagus pan. Once the quinoa is done, add it to the frying pan and toss with the asparagus. Finally, add the lemon juice. Test and add salt and pepper to taste. Serve immediately or as a warm salad.