In small bowl whisk together lemon juice,olive oil,shallot,garlic,oregano,salt and pepper;set aside. Using a vegetable peeler, shave off long,thin strips of zucchini and yellow summer squash. Set a resealable plastic bag in a large bowl and place zucchini,summer squash,mushrooms and sweet pepper in the bag. Marinate vegetables in the refrigerator for 8 hours or overnight, turning bag occasionally. To serve, drain vegetable, reserving marinade. Arrange vegetables on serving plates or a serving platter;drizzle with reserved marinade. Enjoy!!!!