How to Make It
In a large pot of boiling salted water, cook the beans over high heat until crisp-tender, 5 to 6 minutes. Drain the beans and pat dry with paper towels.
Arrange half the pancetta in a single layer in a large skillet and cook over moderate heat, turning once, until golden and crisp, about 6 minutes. Transfer the pancetta to a plate to cool; it will crisp as it cools. Cook the remaining pancetta; let cool. Coarsely crumble the pancetta.
Wipe out the skillet, add the oil and heat until shimmering. Add the shallot and cook over moderate heat until softened, about 4 minutes. Add the beans and cook until tender, about 2 minutes. Add the vinegar and cook until nearly evaporated, about 2 minutes longer. Add the tomatoes and season with salt and pepper. Transfer the vegetables to a platter and garnish with the pancetta. Serve warm or at room temperature.