Combine eggplant, onions, corn, 1 1/2 tablespoons oil, 1/4 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Transfer to one of the prepared baking sheets (reserve the bowl). Roast on the bottom rack for 10 minutes. Combine chicken, zucchini (or squash), garlic and the remaining 1 1/2 tablespoons oil, 1/4 teaspoon salt and 1/4 teaspoon pepper in the reserved bowl. Transfer to the second prepared baking sheet.