Heat a cast iron skillet over over medium heat. Add the sliced bacon. Cook until crispy. Remove bacon from the pan and place on a paper-towel-lined plate.
Drain almost all the bacon fat, leaving about 2-3 tablespoons in the pan. Add the onions and slowly cook down until caramelized.
In a food processor, combine the cooked bacon bits and the caramelized onions. Pulse until it forms a chunky paste. Set aside until needed.
Heat grill pan over medium heat.
Slice the bread into 4 pieces about 3/4-inch thick. Drizzle both sides with a little EVOO. Drizzle the romaine halves as well, and sprinkle with salt and pepper.
Start by grilling the bread until golden and crispy. After you flip the bread, add the romaine to the grill, cooking just until charred, about 1-2 minutes. Remove the bread and romaine from grill.
Thinly slice the romaine on a bias into shreds. Cut the tomatoes into 1/2-inch thick slices.
To assemble, spread a good amount of bacon jam on the hot, grilled bread followed by 3-4 slices of tomato, sprinkle with salt and pepper, then top with the shredded lettuce. Serve warm or room temperature.