Rinse 1 cup of quinoa thoroughly under cold water using a fine-mesh strainer to remove the natural bitter coating.
In a medium saucepan, combine rinsed quinoa with 2 cups of vegetable broth or water. Bring to a boil, then reduce heat to low, cover, and simmer for 15-18 minutes until the liquid is absorbed and the quinoa is tender.
Remove quinoa from heat and let stand, covered, for 5 minutes, then fluff with a fork and allow to cool completely.
While the quinoa cooks, segment your citrus fruits. Using a sharp knife, cut off the top and bottom of each orange and grapefruit. Following the curve of the fruit, slice away the peel and white pith.
Hold the fruit over a bowl to catch juices, and cut between the membranes to release the segments. Reserve 2 tablespoons of the collected juice for the dressing.
In a small bowl, whisk together olive oil, fresh lemon juice, orange zest, honey (or maple syrup), Dijon mustard, and the reserved citrus juice. Season with salt and freshly ground black pepper to taste.
In a large bowl, combine the cooled quinoa, citrus segments, diced avocado, red onion, and chopped mint.
Pour the dressing over the salad and toss gently to combine. Let the salad sit for about 10 minutes before serving to allow the quinoa to absorb the dressing.
Just before serving, fold in the chopped pistachios and crumbled feta (if using). Reserve some for garnishing the top of your salad.