Preheat oven to 400°F (200°C). Grease a baking sheet or line it with parchment paper.
In a large bowl, combine ground chicken, quinoa, Parmesan (if using), parsley, garlic, cumin, oregano, salt, and pepper. Mix well until combined, but avoid overworking the mixture.
Form the mixture into 12 meatballs and place them on the prepared baking sheet.
Bake for 20-25 minutes or until meatballs are cooked through and lightly golden.
While the meatballs cook, prepare the quinoa base: in a large bowl, combine cooked quinoa, cherry tomatoes, cucumber, and spinach. Set aside.
To make the garlic-lemon vinaigrette: In a small bowl, mix together lemon juice, olive oil, and garlic until well combined. Taste and adjust with salt and pepper if needed.
Once the meatballs are done, add them to the quinoa mixture and drizzle with the garlic-lemon vinaigrette.
Serve the bowl topped with lemon slices and optional feta cheese for a creamy finish.