To make the quinoa, place 2 cups water and quinoa in a small saucepan and bring to a boil. Reduce heat to medium low to simmer and cover and cook until all the water is absorbed (about 10 minutes). Remove from heat and set aside to let cool. (You will know quinoa is done when the grain appears soft and translucent and has a fluffy texture.)
Add the cooked quinoa to a medium size bowl, and add the chopped cucumber, tomatoes, and red onion.
To make the dressing, add everything for dressing to a small shaker bottle (or small Tupperware container) and shake to combine. Pour over quinoa mixture and toss to combine. Add feta cheese on top and toss gently. Garnish with parsley if desired. Store in a covered container in the fridge until ready to enjoy, or for up to seven days.