01 - Preheat the oven to 375°F (190°C).
02 - Slice the tops off the bell peppers, remove seeds and membranes. Lightly brush the outside with olive oil and place upright in a baking dish.
03 - Heat 2 tablespoons olive oil in a large skillet over medium heat. Sauté onions until translucent, approximately 3 minutes. Add garlic and cook for 1 minute more.
04 - Add ground beef and cook, breaking apart with a spoon, until browned, about 5 to 6 minutes. Drain excess fat if necessary.
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, cinnamon (optional), salt, and black pepper. Cook for 2 additional minutes.
07 - Remove from heat and fold in half of the crumbled feta cheese.
08 - Spoon the beef mixture evenly into each bell pepper. Pour stock into the bottom of the baking dish to maintain moisture.
09 - Cover the baking dish tightly with aluminum foil and bake for 30 minutes.
10 - Remove foil, sprinkle remaining feta over the peppers, and bake uncovered for an additional 10 minutes until cheese is golden and peppers are tender.
11 - Garnish with chopped fresh parsley and serve with lemon wedges if desired.