Preheat the oven to 400 degrees.
Lay the bell peppers, cut side up in a 9x13 or larger baking dish or on a rimmed cookie sheet. Set aside.
In a small bowl, mix the garlic, olive oil, oregano, salt and pepper. Rub the mixture over the inside of each pepper and on the outside if you have enough to go around.
Bake uncovered until starting to get a little soft 20-25 minutes.
While the peppers bake, bring a bot of salted water to a boil. Add the orzo and cook according to package directions for al dente, drain and transfer to a large bowl.
Add the chicken, balsamic vinegar, olives, feta and maybe a couple of tablespoons of olive oil if it seems a little dry. Set aside.
In another medium bowl toss the tomatoes, olive oil, basil. salt, pepper and red pepper flakes if you are using them. Set aside.
When the peppers are done, pile the orzo and chicken mixture in to each pepper. Add tomatoes on top, or on the side and serve warm or at room temperature.