Bring water and 1 tablespoon olive oil to a boil in a medium pot over high heat. Add couscous; quickly lower heat and let simmer until water is absorbed, 7 to 8 minutes.

Whisk balsamic vinegar, 2 tablespoons olive oil, sugar, salt, and pepper together in a small bowl until dressing is evenly combined.

Fluff couscous with a fork and place in a large, shallow bowl. Add black beans, corn, chicken, and red bell pepper. Fold salad together and pour in the dressing in 3 batches, mixing well after each addition. Refrigerate until chilled, about 30 minutes.