Cook the bacon in a 12-inch skillet over medium heat, turning occasionally, until crisp, 5 to 7 minutes. Transfer to a paper-towel-lined plate and reserve the fat. Cool, crumble, and set aside.
Prepare a high (500°F to 600°F) gas or charcoal grill fire or heat a grill pan over high heat.
Meanwhile, brush both sides of the bread, both sides of each tomato slice, and the cut sides of the romaine with the reserved bacon fat.
Grill the bread, lettuce, and tomato slices until grill marks appear, 1 to 3 minutes per side. Season the lettuce to taste with salt and pepper, cut off the core, and separate the leaves. Season the tomato slices to taste with salt and pepper.
Spread the mayonnaise on one side of each slice of bread. Top the bread with the lettuce, tomato, bacon, and some tarragon, if using. Whisk the oil and lemon juice, drizzle over the sandwiches, and serve.
nutrition information (per serving):
19, Fat Calories
170, Saturated Fat
9, Monounsaturated Fat
24, Polyunsaturated Fat
Photo: Scott Phillips