Brush the burgers with some of the dressing, place them on a barbecue grill set over medium-hot coals, and cook for 5 to 6 minutes on each side, or until the burgers are no longer pink in the center. Meanwhile, slice the tomatoes in half and scoop out the pulp, reserving it. Brush the tomatoes with some of the remaining dressing, place them cut-side down on the grill, and cook until grill marks form, about 3 minutes. Meanwhile, discard the seeds from the pulp, chop the pulp, and place it in a bowl. Coarsely crush the croutons and stir them into the pulp, along with the feta and 1 tablespoon of the remaining dressing. If necessary, add more dressing, 1 teaspoon at a time. Remove the tomatoes from the grill and fill with the crouton mixture. Return the tomatoes to the grill, filled-side up, and continue to cook until the bottoms of the tomatoes have grill marks, about 3 minutes. (For a golden topping, place the tomatoes on a baking sheet and broil under a preheated broiler for 3 minutes, or until the cheese is golden.) Serve the tomatoes with the burgers, placed in the Kaiser rolls.