If using bamboo skewers, soak them in water for at least 30 minutes.
To make the dressing: In a bowl, whisk together the buttermilk, sour cream, lemon juice, 1/4 teaspoon salt and black pepper until smooth.
Prepare the grill for direct cooking over medium heat (350 to 450 degrees).
Thread the tomatoes onto skewers, lightly brush with oil, and season with 1/8 teaspoon salt.
Brush the cut sides of the lettuce quarters with oil, and brush the baguette slices on both sides with oil.
Grill the tomato skewers and lettuce quarters over direct medium heat, with the lid closed, until charred, about 4 minutes, turning the tomatoes as needed and the lettuce once to char on the other cut side. During the last minute of grilling time, toast the baguette slices over direct heat, turning once.