Cook the bacon in a large skillet over medium heat until crisp, 8 to 10 minutes. Transfer to a paper-towel-lined plate. Season the cut sides of the tomatoes with salt.
Heat a grill pan over high heat. Brush the cut sides of the baguette with the olive oil and grill, cut-side down, until toasted, about 2 minutes. Rub the grilled sides with the garlic. Rub just the bottom halves of bread with the tomatoes until most of the juice is absorbed, then top with the tomato skins and season with salt and pepper.
Layer the avocado slices on top of the tomatoes, then add the bacon and frisee. Close with the bread tops.
Photograph by Antonis Achilleos