01 - Set the oven to 375°F (190°C).
02 - Slice tops off bell peppers and remove seeds and membranes. Lightly brush exteriors with olive oil and place upright in a baking dish.
03 - Heat 2 tablespoons olive oil in a large skillet over medium heat. Cook finely chopped onion until translucent, about 3 minutes. Add minced garlic and sauté 1 minute.
04 - Add ground beef to skillet and cook, breaking it apart, until browned, about 5 to 6 minutes. Drain excess fat if needed.
05 - Stir in diced zucchini and tomatoes. Cook for 3 to 4 minutes until softened.
06 - Mix in cooked rice, tomato paste, oregano, basil, smoked paprika, optional cinnamon, salt, and black pepper. Cook for 2 additional minutes.
07 - Remove skillet from heat and fold in half of the crumbled feta cheese.
08 - Fill each bell pepper evenly with the beef mixture. Pour stock into the bottom of the baking dish to maintain moisture.
09 - Cover baking dish with foil and bake for 30 minutes.
10 - Remove foil, sprinkle remaining feta over stuffed peppers, and bake uncovered for 10 more minutes until cheese browns lightly and peppers are tender.
11 - Top with chopped fresh parsley and serve with lemon wedges if desired.