Preheat a rangetop grill or heat a large grill pan or cast-iron skillet. Add the tomatoes, cover with a metal bowl or pot lid and cook over high heat, turning once, until the skins are charred, about 10 minutes. Remove from the heat and let stand, covered, for 30 minutes.
Discard the tomato skins and transfer the tomatoes to a food processor. Add the garlic, 2 tablespoons of water, the olive oil, vinegar, Worcestershire sauce and mustard and process until smooth. Transfer to a bowl and season with salt and pepper. Let the dressing stand at room temperature for 3 to 5 hours. Stir in the parsley just before serving.
The dressing can be refrigerated, covered, for up to 3 days.
One Tablespoon Calories 11 kcal, Protein .1 gm, Carbohydrate .7 gm, Cholesterol 0, Total Fat .9 gm, Saturated Fat .2 gm.