Prepare the grill for direct cooking over medium heat (180º to 230ºC). Preheat a perforated grill pan.
In a large skillet over medium heat on the stove, fry the bacon until crisp, about 10 minutes, turning occasionally. With a slotted spoon, transfer the bacon to paper towels, reserving the bacon fat. Add enough oil to the bacon fat to make 90 milliliters.
In a small bowl mix the shallot, vinegar, thyme, salt, and pepper. Whisk in the bacon fat/oil mixture in a steady stream to make a dressing.
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Lightly coat the tomatoes with some of the dressing. Grill the tomatoes in the grill pan over direct medium heat, with the lid closed, until their skins begin to char and crack, 5 to 6 minutes, shaking the grill pan with tongs to turn them. Wearing insulated barbecue mitts or gloves, carefully remove the grill pan from the grill and pour the tomatoes into a bowl.
Lightly coat the tomatoes with some of the dressing. Grill the tomatoes in the grill pan over medium heat, with the lid closed, until their skins begin to char and crack, 5 to 6 minutes, shaking the grill pan with tongs to turn them. Wearing insulated barbecue mitts or gloves, carefully remove the grill pan from the grill and pour the tomatoes into a bowl.
Brush the cut side of the roll with some of the dressing and grill over direct medium heat, with the lid open, until toasted, about 1 minute. Remove from the grill and cut into large croutons.
Brush the cut side of the roll with some of the dressing and grill over medium heat, with the lid open, until toasted, about 1 minute. Remove from the grill and cut into large croutons.
Arrange the lettuce leaves in a serving bowl. Scatter the tomatoes with their juices and the croutons among the lettuce. Whisk the dressing one more time and spoon some of it over the salad (you may not need all of the dressing). Top with the bacon and finish with the scallions. Serve right away.