Slice off the top quarter (the section with the stem attachment) of the tomato. Using a spoon or melon baller hollow out the tomatoes leaving the outer shell intact. Sprinkle the inside of the tomato with the 1/2 teaspoon salt and turn each tomato upside down on a cooling rack to drain away any loose liquid (it’s a good idea to put a piece of waxed paper or paper towel underneath to catch the drippings). Hold aside until ready to stuff.
While the tomatoes are draining, mix all the vinaigrette ingredients in a large jar, and shake to combine. (You’ll use 1/4 cup for this recipe; reserve the rest for other salads.) You can make this up to three days ahead.
Toast the pine nuts until golden brown and set aside to cool. Dice the mozzarella into 1/2 inch cubes and put into a bowl.
Chop the basil and add to the bowl with the cooled pine nuts. Toss with 1/4 cup of the vinaigrette. Check for seasoning and add more salt and/or pepper as desired.
Invert the tomatoes back upright and stuff, dividing the cheese herb mixture evenly among the four tomatoes.