Chicken and Peppers with Balsamic Vinegar

olive oil, divided

skinless, boneless chicken breast halves - cut into strips

salt and pepper

red bell pepper, thinly sliced

yellow bell pepper, thinly sliced

orange bell pepper, thinly sliced

medium onion, thinly sliced

large cloves garlic, finely chopped

dried basil

balsamic vinegar, divided