01 - Set the oven to 375°F (190°C) to prepare for baking.
02 - Slice the tops off the bell peppers, remove seeds and membranes, lightly brush exteriors with olive oil, and arrange upright in a baking dish.
03 - Heat 2 tablespoons olive oil in a large skillet over medium heat. Sauté onion until translucent, about 3 minutes; then add garlic and cook for 1 minute.
04 - Add ground beef to the skillet, breaking apart with a spoon, and cook until browned, about 5 to 6 minutes. Drain excess fat if necessary.
05 - Stir in zucchini and diced tomatoes; cook until softened, approximately 3 to 4 minutes.
06 - Mix cooked rice, tomato paste, oregano, basil, smoked paprika, cinnamon if using, salt, and pepper into the skillet; cook for an additional 2 minutes.
07 - Remove skillet from heat and fold in half of the crumbled feta cheese.
08 - Spoon the beef mixture evenly into the prepared bell peppers. Pour stock into the bottom of the baking dish to maintain moisture during baking.
09 - Cover the baking dish with foil and bake for 30 minutes.
10 - Remove foil, sprinkle remaining feta cheese over the tops, and bake uncovered for an additional 10 minutes until cheese is lightly browned and peppers are tender.
11 - Optionally garnish with fresh parsley and serve with lemon wedges.