Preheat oven to 400 degrees.
Heat a pan to medium heat and lightly oil.
Add onion and cook about 3 minutes.
Add chicken and cook another 5-6 minutes, or until chicken is cooked mostly through, stirring often.
Add garlic and basil and stir. Cook for 1 minute.
Remove from heat and add to a mixing bowl to cool slightly.
Add feta cheese and mix well.
Add salt and pepper to taste.
Slice off the tops of the peppers and scoop out the innards.
Fill the peppers with your chicken-feta mixture, then set into a lightly oiled baking dish.
Bake for 12-15 minutes, then remove.
Serve!