In a 1-1/2-quart microwave-safe casserole or baking dish, combine zucchini, summer squash, oregano, and olive oil. Cover and microwave on 100 percent power (high) for 4 to 6 minutes or until the squash is just tender, stirring once after 2 minutes cooking.
Sprinkle Parmesan over vegetables; toss. Serve warm. Makes 4 side-dish servings.