Wash and dry the peppers. The slice them length ways and then in half so they fit in the pan easily.
In a frying pan large enough to hold all the peppers heat the olive oil until hot. Place all the peppers cut side down. If they all don't touch the bottom of the pan don't worry, they will shrink as they cook.
Saute on high heat for about 4 or 5 minutes and then turn them all over. A long metal tong helps here. Keep repeating this until all the peppers have taken a good color about 20 minutes
A few minutes before they are done add the sugar, garlic and balsamic vinegar and mix well. Let the vinegar concentrate a little and the garlic flavor the peppers.
Salt and pepper them to taste.
Adding the garlic late in the cooking helps to avoid it from burning. The steam from the balsamic vinegar also helps the flavors to permeate the vegetables.