To make couscous, heat oil in a medium pot. Add onion and saute for 1-2 minutes until soft and translucent.
Add in couscous and toss everything together, ensuring your couscous is covered by the oil and onion mixture. Stir to toast them for about 2 minutes.
Pour in broth and season with salt and pepper. Bring to a simmer and cook, covered for 10 minutes.
Fluff with fork and let cool.
To make vinaigrette, place all ingredients in a bowl and whisk until creamy.
To assemble salad, toss cooled couscous with spring mix, spinach, green onions and mint leaves. Place on platter, top with radishes, feta and drizzle with dressing.