Cook pancetta in a large skillet over medium-high heat, stirring frequently until crisp, about 5 minutes. Remove pancetta with a slotted spoon and drain on paper towels; reserve drippings in pan.
Add shallots to the skillet drippings; cook over medium-high heat until golden brown, about 6 minutes. Add balsamic vinegar and cook for 1 minute. Remove from heat.
Place green beans in large pot of lightly salted, boiling water. Cook until just crisp-tender, 5-6 minutes. Drain immediately and add green beans to shallot mixture; season with salt and pepper. Toss until coated, place in dish, sprinkle pancetta over top, and serve.