Season chicken with salt and pepper (I also seasoned with onion powder, garlic powder, dried basil, and crushed red pepper for more flavor.)
In a skillet, saute a 1/4 of the garlic and onion until translucent and add chicken. Cook until JUST done. Transfer to a plate a keep warm.
Add the remaining oil, garlic, onion and peppers. Saute until softened. (Add a bit of water or chicken broth if the liquid evaporates too much.) Add basil and balsamic vinegar. Return chicken and juices to pan. Reduce heat and simmer for another couple minutes.