Chop tomatoes, cucumber, and feta into cubes and thinly slice mint leaves. (You can do this ahead of time and put them in the refrigerator until you are ready to combine with couscous.)
When onions become translucent, add couscous to toast for about 2-3 min. Stir often.
Pour simmering stock over couscous, reduce heat to a simmer, place lid, and allow to cook for 8-10 min.
While couscous is cooking, make the dressing by combining all ingredients into a tall narrow glass jar. With a hand blender, blend all ingredients until creamy.
Fluff cooked couscous with a fork to separate.
Place all ingredients in a large bowl and mix together.
Notes
Can be served with grilled chicken or grilled steak skewers.