In a large mixing bowl, combine ground chicken, breadcrumbs, Parmesan cheese, beaten egg, minced garlic, chopped rosemary, olive oil, salt, pepper, and optional red pepper flakes. Mix gently until just combined—avoid overmixing to keep the meatballs tender. Form the mixture into 1-inch meatballs and place on a lined baking sheet. Chill in the refrigerator for 30 minutes.

In a large skillet over medium heat, warm a tablespoon of olive oil, then sauté finely chopped onion until softened and translucent, about 3-4 minutes. Add minced garlic and cook for another 30 seconds until fragrant. Stir in crushed tomatoes, tomato sauce, dried oregano, dried basil, and a pinch of salt and pepper. Allow the sauce to simmer gently for about 10 minutes.

Incorporate the orzo pasta and chicken broth into the tomato sauce, stirring well. Bring the mixture to a boil, then reduce the heat to low, cover, and let it simmer for 10-12 minutes until the orzo is tender.

Preheat your oven to 400°F (200°C). To bake, place the meatballs on a lined baking sheet and bake for 20-25 minutes or until cooked through and reach an internal temperature of 165°F. Alternatively, pan-fry the meatballs for 8-10 minutes, turning occasionally for even browning.

Once the meatballs are cooked and the orzo has absorbed the sauce, transfer the meatballs into the skillet with the tomato orzo. Let them simmer together for a couple of minutes to marry the flavors. Serve hot, garnished with fresh basil leaves and grated Parmesan cheese.