Preheat the oven to 400 degrees and line a baking sheet with parchment paper. Add the squash ingredients to the baking sheet and toss to coat evenly. Place in the oven and roast for 20 minutes. Toss and cook for another 5-10 minutes, or until fork tender and slightly charred.
Meanwhile, make the couscous. Heat the oil in a skillet over medium heat. Add the couscous and toast for about 3 minutes, or until slightly browned - stirring frequently. Pour in the broth & dry seasonings. Bring to a boil, lower the heat and cover. Simmer for 15-20 minutes, or until all of the liquid is absorbed. Allow to cool slightly before adding to the salad.
Add all of the dressing ingredients to a bowl and whisk to combine. Taste and adjust seasonings as needed. Set aside.
To assemble, add the couscous, squash, tomatoes, onion, feta, corn, cilantro and avocado* to a large bowl. Pour the dressing over the salad and toss to combine. Serve chilled or at room temperature with the optional toppings.
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Notes
*Wait to add the avocado until right before serving to keep it from browning.