Rinse quinoa until there are no small foamy bubbles and the water runs clear, approximately 1 minute, then drain.
Add quinoa and 2 cups stock to a saucepan (at least 2 quarts). Bring to a boil, then reduce to a simmer on the lowest possible setting. Cover pot with a lid and simmer 15-20 minutes, or until the liquid has evaporated.
While quinoa is cooking: combine onion, corn, bell pepper, black beans and cherry tomatoes in a large mixing bowl. Make vinaigrette by combining all ingredients in a blender and blending until smooth and creamy. Refrigerate.
When quinoa is finished cooking, remove pot from the heat but keep covered 5 minutes. After 5 minutes, uncover and fluff with a fork. Add quinoa to the large mixing bowl with other ingredients.
Grab vinaigrette from the fridge and pour half of it over your salad, tossing to coat. Refrigerate salad for at least 2 hours and up to overnight. Once you’re ready to serve, toss salad with however much extra vinaigrette you want (I use it all), cilantro and pumpkin seeds, if using. Taste and add salt accordingly. Leftover salad will keep tightly sealed in the fridge up to 4 days.