01 - Set oven to 375°F.
02 - Trim tops off peppers, remove seeds and membranes, and arrange upright in a baking dish.
03 - Heat olive oil in a large skillet over medium heat, add chopped onion and cook until softened, about 4 minutes.
04 - Stir in minced garlic, cook 1 minute, then add ground beef. Brown and cook through, breaking it apart for 6–7 minutes.
05 - Add cherry tomatoes, drained diced tomatoes, cumin, smoked paprika, oregano, salt, and black pepper. Simmer 5 minutes until liquid mostly evaporates.
06 - Remove from heat; fold in cooked rice, crumbled feta, chopped parsley, and pine nuts if using.
07 - Divide beef mixture evenly among peppers, gently packing the filling.
08 - Optionally replace tops on peppers. Pour 2 to 3 tablespoons water into the bottom of the dish.
09 - Cover dish with foil and bake for 30 minutes.
10 - Remove foil and bake another 15 minutes until peppers are tender and lightly browned on top.
11 - Let rest 5 minutes before serving. Garnish with extra parsley if desired.