Preheat the oven to 425°F (220°C). Lightly grease a 9x13 or 2-quart baking dish or large rimmed baking sheet with olive oil.
In a large mixing bowl combine the potatoes and onions with 2 tablespoons of oil, 1 teaspoon salt, ½ teaspoon Italian seasoning, ½ teaspoon garlic powder, ½ teaspoon pepper, and a pinch of red pepper flakes. Stir well.
Spread the seasoned potatoes and onions out in a single layer in the prepared pan. Bake for 20 minutes, or until the potatoes are nearly fork-tender.
While the potatoes are roasting, add the squash, zucchini, bell peppers, peeled garlic, and cherry tomatoes to the same mixing bowl. Add the remaining tablespoon of olive oil, 1 teaspoon salt, ½ teaspoon Italian seasoning, ½ teaspoon garlic powder, ½ teaspoon pepper, and a pinch of red pepper flakes. Toss to coat.
Remove the potatoes from the oven, flip them, and then add the seasoned vegetables on top of the potatoes. Return to the oven.
Roast for an additional 15 to 20 minutes, or until the vegetables are fully cooked and slightly caramelized.
Serve warm with fresh Parmesan cheese if desired.
