Preheat oven to 375°F (190°C).
In a large baking dish, layer the potatoes, carrots, zucchini, and yellow squash. Drizzle with olive oil and sprinkle with salt and pepper.
In a medium bowl, combine the cream, Parmesan cheese, and garlic powder, if using. Pour the mixture over the vegetables.
Bake for 45-50 minutes, or until vegetables are tender and the cheese sauce is golden brown and bubbly.
Let cool for 5 minutes before serving.