Preheat the oven. Set to 400°F (200°C).
Lightly oil a baking dish that will fit the peppers snugly.
Par-cook the peppers. Place hollowed peppers cut side up in the dish. Brush or spray with a little olive oil and sprinkle with a pinch of salt. Bake for 10–12 minutes to soften slightly.
Set aside.
Cook the quinoa. In a small pot, bring chicken broth to a boil. Stir in rinsed quinoa, reduce heat to low, cover, and simmer 15 minutes, or until liquid is absorbed. Fluff with a fork.
Sauté the aromatics. Heat 1 tablespoon olive oil in a large skillet over medium.
Add onion and cook 3–4 minutes until translucent. Add garlic and cook 30 seconds, just until fragrant.
Brown the chicken. Add ground chicken, breaking it up with a spatula. Season with salt, pepper, cumin, smoked paprika, oregano, and chili flakes.
Cook 5–6 minutes until no longer pink.
Add veggies and tomatoes. Stir in diced zucchini and drained tomatoes. Cook 3–4 minutes to soften and reduce excess moisture.
Combine with quinoa. Remove skillet from heat. Fold in cooked quinoa, half the cheese, chopped herbs, and lemon juice.
Taste and adjust salt, pepper, or spices. The mixture should be well-seasoned and slightly juicy, not dry.
Fill the peppers. Spoon the mixture into the par-cooked peppers, mounding slightly. Sprinkle the remaining cheese on top.
Bake. Return to the oven for 15–18 minutes, until the peppers are tender and the cheese is melted and lightly golden.
Rest and serve. Let the peppers sit 5 minutes.
Garnish with extra herbs. Serve with a simple green salad, yogurt or sour cream, and a squeeze of lemon if you like.