Prepare the Peppers: Preheat your oven to 400°F (200°C). Slice the tops off the bell peppers. Carefully remove the seeds and white membranes from the inside. Arrange the peppers standing up in a 9x13-inch baking dish. Drizzle 1 tablespoon of the olive oil over the peppers, rubbing it lightly to coat the outsides. Bake for 15 minutes to soften them slightly.
Build the Aromatic Base: While the peppers are pre-baking, heat the remaining 2 tablespoons of olive oil in a large skillet over medium heat. Add the chopped onion and cook until softened, about 5-6 minutes. Add the minced garlic, smoked paprika, cumin, oregano, and cinnamon. Cook for another minute until fragrant, stirring constantly.
Cook the Protein: Add the ground chicken to the skillet. Break it up with a spoon and cook until no longer pink, about 6-7 minutes. Season generously with freshly ground black pepper.
Combine the Filling: Pour the undrained fire-roasted tomatoes and the rinsed chickpeas into the skillet. Stir to combine and bring the mixture to a gentle simmer for 2 minutes.
Finish the Filling: Remove the skillet from the heat. Fold in the cooked farro, ½ cup of fresh parsley, fresh mint, and the lemon zest. Stir until everything is well combined.
Stuff and Bake: Remove the pre-baked peppers from the oven. Carefully spoon the filling evenly into each pepper, packing it in gently. Cover the baking dish tightly with aluminum foil. Return to the oven and bake for 25 minutes.
Add Feta and Finish: After 25 minutes, remove the foil. Sprinkle the crumbled feta cheese evenly over the top. Return the dish to the oven, uncovered, and bake for an additional 10-15 minutes, or until the peppers are fork-tender and the feta is slightly golden.
Rest and Serve: Let the peppers rest for 5 minutes before serving. Garnish with additional fresh parsley and serve warm.