Preheat your oven to 425°F (220°C). This high temperature will help achieve a nice caramelization on the vegetables.

Wash the zucchini and yellow squash under cold water to remove any dirt. Pat them dry with a clean kitchen towel.

Using a chef's knife, slice the zucchini and yellow squash into 1/4-inch thick rounds. Uniform slices ensure even cooking.

In a mixing bowl, combine the sliced zucchini and yellow squash. Drizzle with olive oil and sprinkle with garlic powder, dried oregano, salt, and black pepper.

Toss the vegetables gently until they are evenly coated with the oil and seasonings. This step is crucial for flavor distribution.

Spread the seasoned vegetables in a single layer on a baking sheet. Overcrowding the pan can lead to steaming instead of roasting.

Place the baking sheet in the preheated oven and roast for 20-25 minutes, or until the vegetables are tender and slightly browned. Stir halfway through to ensure even cooking.

Once roasted, remove the baking sheet from the oven. If desired, sprinkle with grated Parmesan cheese while the vegetables are still hot for added flavor.

Serve immediately as a side dish to your favorite protein or enjoy as a healthy snack.