How to Make It
Light a grill or preheat a grill pan to medium-high. In a medium bowl, toss the tomatoes with 1 tablespoon of the olive oil. Grill, turning, until blistered and lightly charred, 5 to 7 minutes. Let cool slightly.
In a food processor, combine the grilled tomatoes with the vinegar, lemon juice and mustard and pulse to blend. With the machine on, slowly drizzle in the remaining 1/2 cup of olive oil. Transfer the vinaigrette to a medium bowl, stir in the parsley and season with salt and pepper.