Preheat the oven to 400 degrees F.
In a large bowl, whisk together the cumin, paprika sumac, salt and pepper with olive oil. Add the vegetables, tossing them in the marinade.
Roast the vegetables until they are lightly browned at the edges and tender in the middle, flipping and tossing halfway through roasting, about 30-35 minutes.
Stir together the couscous, roasted vegetables, scallions, parsley, pistachios and feta. Drizzle in the vinaigrette and stir to combine all the ingredients.