Prepare the tahini by placing all ingredients in a blender and purée until creamy. If the mixture becomes very thick, add some water to dilute, so that it can be easily poured over the salad.
Place the quinoa into a pot of boiling, salted water and let it boil for 15 minutes, until tender. Drain and cool with cold water. Allow the quinoa to drain well.
Transfer quinoa to a bowl and mix with the beans, corn, tomatoes, avocado, feta cheese, salt and pepper.
Place the salad on a platter, scatter the spinach leaves on the salad, drizzle with tahini sauce and serve.
This salad can also be served as a wrap. Prepare a thicker tahini sauce by reducing the water. Smear the sauce on a tortilla and add 2-3 tbsp of the quinoa salad on one side. Place a few spinach leaves on top, wrap the tortilla tightly and serve.