Make the basil vinaigrette. Place all dressing ingredients in a blender, then purée until very smooth. Transfer to a bowl then set aside.
Grill the veggies. If you have a grill basket, you can cut the zucchini, squash, and red onion into 1-inch bite-size pieces. If not, you’ll want to grill them in large pieces and then cut. I’ll include both directions below.
If you have a grill basket: Preheat a grill to medium-high with a grill basket directly on top of the grates until it’s about 450F. Coat with grill spray, then add chopped zucchini, yellow squash, whole tomatoes, and chopped red onion. Sprinkle with 2-3 tsp kosher salt then cook, stirring occasionally, until the vegetables are charred and tender, about 7-10 minutes. It’s ok if some of the tomatoes burst! Using grill gloves or oven mitts, carefully remove the grill basket, then transfer the grilled veggies to a very large mixing bowl.
If you do NOT have a grill basket. Preheat a grill to medium-high with a large cast-iron skillet directly on top of the grates until it’s about 450F. Coat with grill spray, then add chopped zucchini, yellow squash, whole tomatoes, and chopped red onion. You will likely have to cook this in two batches. Sprinkle with half of the kosher salt then cook, stirring occasionally, until the vegetables are charred and tender, about 7-10 minutes. Using grill gloves or oven mitts, carefully remove the skillet, then transfer the grilled veggies to a very large mixing bowl. Repeat with remaining vegetables until all are grilled, seasoning with remaining salt to taste.
Cook the couscous. Bring 3 cups of water to a rapid boil over high heat. Add 2 cups of dry couscous and ½ tsp kosher salt, then return to a boil. Immediately reduce the temperature to a simmer, then cover the pan and cook for 15-17 minutes. Remove the lid, then use a fork to fluff the couscous. All of the water should be absorbed – if there’s extra for any reason, simply drain it. The couscous should be tender.
Toss with dressing, then serve! Add the cooked couscous directly on top of the grilled veggies. Add 3 cups baby arugula, then pour the basil vinaigrette on top. The heat from the warm couscous will wilt the arugula. Sprinkle with most of the chives, reserving a few for garnish, then toss to thoroughly coat. Taste, adjust seasoning as needed, adding flaky sea salt and black pepper to taste, then finish with a little extra arugula on top. Garnish with remaining chives. Enjoy hot, room temperature, or cold!