To make the balsamic reduction, add balsamic vinegar and brown sugar to a small saucepan over medium heat. Bring to a slight boil and reduce by half, about 6-8 minutes; set aside and let cool.

Heat olive oil in a medium skillet over medium high heat.

Season chicken breasts with salt and pepper, to taste. Add to skillet and cook, flipping once, until cooked through, about 3-4 minutes per side. Let cool before dicing into bite-size pieces.

To assemble the salad, place romaine lettuce in a large bowl; top with chicken, mozzarella, tomatoes, avocado and basil. Pour balsamic reduction on top of the salad and gently toss to combine.

Serve immediately.