6 thin slices pancetta (about 2 ounces)
1/4 cup balsamic vinegar
1/4 cup extra-virgin olive oil
Kosher salt and freshly ground black pepper
3 large tomatoes, quartered and chopped into 1-inch pieces
1 English cucumber, halved lengthwise and thickly sliced
1/2 red onion, cut into 1-inch pieces
Be sure to store tomatoes at room temperature -- refrigerating them can make them mealy. They'll continue ripening as they sit on the counter.