In a large bowl, whisk together lemon juice, soy sauce, oil, parsley, garlic, salt, and pepper. Add the scallops and mushrooms and coat well. Cover and marinate in the refrigerator for at least 1 hour but no more than 3 hours, turning occasionally. Heat griller. Using a slotted spoon, transfer scallops and mushrooms to a lightly oiled griller pan. Grill 5 inches from heat for 4 minutes. Turn, brush with marinade, and grill 4 minutes more or until cooked through. Garnish with lemon wedges and serve.