Preheat oven to 450 degrees F.
Season the squash with salt and pepper, drizzle with 4 tablespoons olive oil, and place in a single layer on 1 or 2 cookie sheets.
Bake in the oven until just tender, about 18 to 20 minutes. Meanwhile, stir together the remaining oil, vinegar, onion, chile flakes, oregano, and garlic and season with salt and pepper. Remove the squash from the oven and pour the marinade over. Allow to cool for 20 minutes in the marinade, sprinkle with fresh mint leaves, and serve. This dish can be made earlier in the day but should not be refrigerated.