To make the vinaigrette, combine all the ingredients in a small bowl and whisk well. Set aside.
Slice vegetables and drizzle them with olive oil. Season them with oregano, salt, and pepper, then toss to coat evening. Using a grill pan or an actual grill, place vegetables onto hot grill and cook about 4 minutes on each side for the squash, and about 5-6 minutes for bell peppers and onion, or until tender. Set vegetables aside and let them cool before dicing.
After couscous is cooked according to instructions, drain well, then pour into a large bowl. Add the diced veggies, feta, then drizzle with half of the vinaigrette to start, and toss to coat evening. Add more vinaigrette as you prefer. Serve cold or at room temperature. Enjoy!