How to Make It
Preheat the oven to 350°. Spread the baguette slices on a large rimmed baking sheet and bake for about 8 minutes, or until just crisp. Let cool.
In a large skillet, heat the olive oil. Add the pancetta slices in an even layer and cook over moderate heat until crisp, about 2 minutes per side. Drain on paper towels and crumble.
In a medium bowl, mix the shrimp with the mayonnaise, basil and lemon juice and season with salt and pepper.
Spread a thin layer of mayonnaise on each of the baguette slices. Top with an arugula leaf, a slice of tomato and a scant tablespoon of the shrimp salad. Sprinkle with the crumbled pancetta and serve.