Cut eggplant into 1-inch cubes, bell peppers into 1-inch pieces, halve the cherry tomatoes, and roughly chop the red onion. Spread all vegetables on a large roasting pan or sheet pan. Drizzle with olive oil, then sprinkle with chili pepper flakes, garlic powder, and salt to taste. Toss everything together until vegetables are evenly coated with oil and seasoning.

Preheat oven to 425°F (220°C). Place the pan of seasoned vegetables in the oven and roast for 12-15 minutes. Stir the vegetables halfway through cooking to ensure even browning and caramelization on all sides. Continue roasting until the edges are deeply browned and the vegetables are tender, about 25-30 minutes total. I like to listen for a slight sizzle when I stir—it means the vegetables are getting those delicious caramelized edges that build real flavor.

Remove the pan from the oven and let it cool for 2-3 minutes so it's warm but not piping hot. Drain and rinse the chickpeas, then add them to the warm roasted vegetables along with the basil pesto and red wine vinegar. Stir gently but thoroughly to coat everything evenly with the pesto and vinegar, allowing the flavors to meld while the vegetables are still warm. This timing is important—the warmth helps the pesto distribute and the vegetables absorb the flavors better.

Add the arugula to the warm vegetable mixture and stir gently until the leaves begin to wilt from the residual heat—this usually takes just 30 seconds to 1 minute of stirring. The warmth will soften the arugula while keeping it tender and bright, and it helps the peppery flavor blend with the roasted vegetables. Taste and adjust seasoning with additional salt if needed. Serve while still warm or at room temperature, as preferred.