Gather all ingredients.

Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add chicken and season with salt and pepper; cook and stir until golden brown, about 3 to 5 minutes. Transfer chicken into a bowl; set aside.

Heat remaining oil in the same skillet; stir in bell peppers and onion. Cook and stir until tender, about 3 minutes.

Add garlic; cook and stir until fragrant. Stir in 2 tablespoons balsamic vinegar and basil.

Add chicken back into the skillet; reduce heat to low, cover, and simmer until chicken is no longer pink and juices run clear, about 20 minutes.

Stir in remaining balsamic vinegar just before serving.