In a small bowl, combine the Parsley, Olive Oil, Red Wine Vinegar,Mustard, Sugar, Salt, Pepper and Garlic. Whisk until well combined and pour over the Tomatoes and Onions. Gently fold until all the Tomatoes and Onions are well coated. Cover with plastic wrap and set aside for 20 minutes at room temperature, then serve. Bet there will not be one single bite left!