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.