In a medium size bowl, combine peppers, onion, and chopped basil. In a small size bowl combine olive oil, balsamic vinegar, garlic, salt, red pepper flakes, and fresh ground pepper and stir to combine.
Pour olive oil mixture into medium sized bowl and gently stir to combine. Cover and refrigerate 2 hours to allow flavors to blend. Salsa is at its best when eaten within 24 hours.