Pre-heat oven to 350 degrees. Spread the baguette slices on large rimmed baking sheet and bake until crisp, cool.
In a large skillet, heat the olive oil and 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 very thin layer of mayonnaise on each baguette slice. Top with an arugula leaf, a slice of tomato and a tablespoon of shrimp salad. Sprinkle the crumbled pancetta on top and serve.
Adapted from recipe by Alex Freij, from "Vodka - Still Crazy After all These Years"