Start by combining ground chicken, rosemary, garlic, breadcrumbs, parmesan, egg, olive oil, salt, and pepper in a bowl. Mix gently using your hands until just combined. Avoid overmixing, as it can make the meatballs dense instead of tender.
Form the mixture into small, evenly sized balls and place them on a lined baking sheet. Bake in a preheated oven at 400°F (200°C) for about 20 minutes. The meatballs should be golden and fully cooked through.
In a large skillet, melt butter and sauté chopped onion until soft and fragrant. Add garlic and cook briefly before pouring in crushed tomatoes and chicken broth. Stir well and bring the mixture to a gentle simmer.
Stir the orzo directly into the tomato mixture and let it cook uncovered. Stir occasionally to prevent sticking and ensure even cooking. The orzo will absorb the sauce and become creamy.
Once the orzo is tender, nestle the baked meatballs into the pan. Let everything simmer together for a few minutes so the flavors blend beautifully. Garnish with fresh parsley before serving.