Combine rinsed quinoa and chicken broth in a medium saucepan, bring to a boil over medium-high heat, then reduce to low, cover, and cook for 15 minutes. Remove from heat and let sit covered for 5 minutes, then fluff with a fork and set aside.
Preheat oven to 375°F (190°C). Halve each bell pepper lengthwise, remove seeds and membranes, lightly brush the insides with olive oil and a pinch of salt, then arrange cut-side up in a lightly oiled 9x13 inch baking dish.
Heat 1 tablespoon olive oil in a large skillet over medium-high heat, add the ground turkey in a single layer, let it sit undisturbed for 2 minutes, then break it into crumbles and cook until no pink remains, about 5–7 minutes total. Drain off any excess liquid, season with salt and pepper, and transfer to a bowl.
In the same skillet over medium heat, cook the diced onion until soft and translucent, about 3–4 minutes, then add the garlic and stir for 30–60 seconds until fragrant. Add the zucchini and cook for 2–3 minutes, then stir in the drained diced tomatoes and cook for another 1–2 minutes.
Return the browned turkey to the skillet, add the cooked quinoa, and sprinkle in all the spices (cumin, smoked paprika, chili powder, oregano, red pepper flakes). Stir well to combine, taste and adjust seasoning, then stir in the lime juice if using.
Divide the filling evenly among the 6 pepper halves, mounding it slightly above the rim and pressing gently to pack it in. Sprinkle half the shredded cheese (about ½ cup) over the tops.
Cover the baking dish tightly with aluminum foil and bake at 375°F (190°C) for 25 minutes until the peppers begin to soften and the filling is heated through.
Remove the foil, sprinkle the remaining ½ cup of cheese over the peppers, and return to the oven uncovered for 8–10 minutes until the cheese is melted, bubbly, and lightly golden at the edges.
Let the stuffed peppers rest for 5 minutes out of the oven, then sprinkle with fresh chopped parsley or cilantro and serve immediately.