Position 1 rack in bottom third of oven and 1 rack in center of oven and preheat to 400°F. Spray 2 heavy large baking sheets with nonstick spray. Combine all remaining ingredients except garlic in very large bowl; toss to coat. Season generously with salt and pepper. Divide vegetable mixture between prepared sheets. Place 1 sheet on each oven rack. Roast 30 minutes, stirring occasionally. Reverse positions of baking sheets. Add 5 garlic cloves to each baking sheet.
Continue to roast until all vegetables are tender and brown in spots, stirring and turning vegetables occasionally, about 45 minutes longer. (Can be prepared 4 hours ahead. Let stand on baking sheets at room temperature. Rewarm in 450°F oven until heated through, about 15 minutes.)
Transfer roasted vegetables to large bowl and then serve.