Rinse 1 cup of quinoa thoroughly in a fine mesh strainer to remove bitterness. Combine rinsed quinoa with 2 cups of water in a pot. Now, bring to a boil, then reduce heat, cover, and simmer for 15 minutes or until water is absorbed. Remove from heat and let it sit, covered, for 5 minutes. Fluff with a fork.
Heat 1 tbsp olive oil in a large skillet over medium heat. Add diced onion and cook for 2–3 minutes until softened. Stir in minced garlic and cook for another 30 seconds. Now, add ground turkey, breaking it up with a spatula, and season with Italian herbs, smoked paprika, salt, and pepper. Cook for 6–8 minutes until turkey is browned and fully cooked. Remove from heat.
In the same skillet, add chopped bell pepper and zucchini. Sauté for 3–4 minutes until just tender. Add baby spinach and stir until wilted (about 1 minute). Mix cooked vegetables into the turkey mixture.
Preheat oven to 375°F (190°C). In a large bowl, combine the cooked quinoa with the turkey and veggie mixture. Stir in half of the shredded cheese. Now, transfer the mixture into a lightly greased 9×13-inch baking dish. Sprinkle the remaining cheese (and Parmesan, if using) evenly on top.
Bake uncovered for 20–25 minutes, or until cheese is melted and bubbly. And, for a golden finish, broil the casserole for an additional 2–3 minutes, watching closely. Let cool for 5–10 minutes before slicing and serving.