Heat the oil in medium high in a skillet or heavy frying pan. Add the chopped onion and garlic and saute until aromatic or about 1 minute.
Add the sliced zucchini and sauté for about 5 minutes or until the the sliced zucchinis are cooked but not mushy. Season with salt and pepper. Toss with the freshly squeezed lemon juice. Serve immediately sprinkled generously with grated Parmesan cheese!