Preheat the oven to 425°F. Trim and dice the eggplant, bell peppers, zucchini, and red onion into 1-inch cubes. Collect the vegetables on two large rimmed baking sheets. Drizzle the vegetables with oil, oregano, salt, and pepper, and toss to coat well. Spread them in a single layer and roast for 25-30 minutes, rotating halfway through, until browned. Remove to cool.

Bring a large pot of salted water to a boil. Cook the orzo according to package instructions. Drain and rinse. Transfer to a large mixing bowl and let it cool.

Drizzle the oil, lemon zest and juice, salt, pepper, and cayenne over the cooled orzo and stir. Add the cooled roasted vegetables and herbs, stirring again. Crumble in the feta cheese and season to taste with white wine vinegar if desired.

Serve at room temperature, or keep chilled in the fridge for up to a week.