Preheat oven to 450°F (230°C). In a small bowl, combine oil, garlic powder, paprika, oregano, salt and pepper. Stir to combine.
Use half the spiced oil to brush all over the peppers and then arrange on a large cookie sheet with the open side facing up. Transfer to the oven and cook for 20 minutes, or until peppers start to get charred in spots.
While the peppers are cooking, bring water to a boil in a large pot or saucepan. Add orzo and bring to a simmer, then reduce heat, cover and cook for an additional 15 minutes, or until most of the liquid has been absorbed and orzo is tender.
Add spinach, lemon juice, garlic, chickpeas, tomatoes, olives, shallot, feta, and red pepper flakes to the pot. Stir to combine and remove from heat.
When peppers are cooked, stuff the orzo mixture into each pepper. Sprinkle with additional feta and fresh basil, if desired. Serve immediately.