Preheat the oven to 425°F and line a large baking sheet with parchment paper.
Add the squash, mushrooms, bell pepper, red onion, zucchini, and baby corn to a large mixing bowl.
Pour the chimichurri sauce over the vegetables and toss until everything is evenly coated.
Spread the vegetables out in a single layer on the prepared baking sheet. Roast for 25–30 minutes, stirring halfway through, until the vegetables are tender and starting to brown.
Transfer to a serving dish and garnish with extra chimichurri if desired.